@c DO NOT EDIT!  Generated automatically by munge-texi.

@c Copyright (C) 1996, 1997, 2007 John W. Eaton
@c
@c This file is part of Octave.
@c
@c Octave is free software; you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by the
@c Free Software Foundation; either version 3 of the License, or (at
@c your option) any later version.
@c 
@c Octave is distributed in the hope that it will be useful, but WITHOUT
@c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
@c FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
@c for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with Octave; see the file COPYING.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Control Theory
@chapter Control Theory

The Octave Control Systems Toolbox (@acronym{OCST}) was initially developed
by Dr.@: A. Scottedward Hodel 
@email{a.s.hodel@@eng.auburn.edu} with the assistance
of his students
@itemize @bullet
@item R. Bruce Tenison @email{btenison@@dibbs.net}, 
@item David C. Clem,
@item John E. Ingram @email{John.Ingram@@sea.siemans.com}, and 
@item Kristi McGowan.  
@end itemize
This development was supported in part by @acronym{NASA}'s Marshall Space Flight 
Center as part of an in-house @acronym{CACSD} environment.  Additional important 
contributions were made by Dr. Kai Mueller @email{mueller@@ifr.ing.tu-bs.de}
and Jose Daniel Munoz Frias (@code{place.m}).

An on-line menu-driven tutorial is available via @code{DEMOcontrol};
beginning @acronym{OCST} users should start with this program. 

@anchor{doc-DEMOcontrol}
@deftypefn {Function File} {} DEMOcontrol
Octave Control Systems Toolbox demo/tutorial program.  The demo
allows the user to select among several categories of @acronym{OCST} function:
@example
@group
octave:1> DEMOcontrol
Octave Controls System Toolbox Demo

  [ 1] System representation
  [ 2] Block diagram manipulations
  [ 3] Frequency response functions
  [ 4] State space analysis functions
  [ 5] Root locus functions
  [ 6] LQG/H2/Hinfinity functions
  [ 7] End
@end group
@end example
Command examples are interactively run for users to observe the use
of @acronym{OCST} functions.
@seealso{Demo Programs: bddemo.m, frdemo.m, analdemo.m,
moddmeo.m, rldemo.m}
@end deftypefn


@menu
* sysstruct::                   
* sysinterface::                
* sysdisp::                     
* blockdiag::                   
* numerical::                   
* sysprop::                     
* systime::                     
* sysfreq::                     
* cacsd::                       
* misc::                        
@end menu

@node sysstruct
@section System Data Structure

@menu
* sysstructvars::               
* sysstructtf::                 
* sysstructzp::                 
* sysstructss::                 
@end menu

The @acronym{OCST} stores all dynamic systems in
a single data structure format that can represent continuous systems,
discrete-systems, and mixed (hybrid) systems in state-space form, and
can also represent purely continuous/discrete systems in either
transfer function or pole-zero form. In order to
provide more flexibility in treatment of discrete/hybrid systems, the
@acronym{OCST} also keeps a record of which system outputs are sampled.

Octave structures are accessed with a syntax much like that used
by the C programming language.  For consistency in
use of the data structure used in the @acronym{OCST}, it is recommended that
the system structure access m-files be used (@pxref{sysinterface}).
Some elements of the data structure are absent depending on the internal
system representation(s) used.  More than one system representation
can be used for @acronym{SISO} systems; the @acronym{OCST} m-files ensure that all representations
used are consistent with one another.

@anchor{doc-sysrepdemo}
@deftypefn {Function File} {} sysrepdemo
Tutorial for the use of the system data structure functions.
@end deftypefn


@node sysstructvars
@subsection Variables common to all @acronym{OCST} system formats

The data structure elements (and variable types) common to all  system
representations are listed below; examples of the initialization
and use of the system data structures are given in subsequent sections and
in the online demo @code{DEMOcontrol}.
@table @var
@item n
@itemx nz
The respective number of continuous and discrete states
in the system (scalar)

@item inname
@itemx outname
list of name(s) of the system input, output signal(s). (list of strings)

@item sys
System status vector.  (vector)

This vector indicates both what representation was used to initialize
the system data structure (called the primary system type) and which
other representations are currently up-to-date with the primary system
type (@pxref{structaccess}).

The value of the first element of the vector indicates the primary
system type.

@table @asis
@item 0
for tf form (initialized with @code{tf2sys} or @code{fir2sys})

@item 1
for zp form (initialized with @code{zp2sys})

@item 2
for ss form (initialized with @code{ss2sys})
@end table

The next three elements are boolean flags that indicate whether tf, zp,
or ss, respectively, are ``up to date" (whether it is safe to use the
variables associated with these representations).  These flags are
changed when calls are made to the @code{sysupdate} command.

@item tsam
 Discrete time sampling period  (nonnegative scalar).
 @var{tsam} is set to 0 for continuous time systems.

@item yd
 Discrete-time output list (vector)

 indicates which outputs are discrete time (i.e.,
    produced by D/A converters) and which are continuous time.
    yd(ii) = 0 if output ii is continuous, = 1 if discrete.
@end table

The remaining variables of the  system data structure are only present
if the corresponding entry of the @code{sys} vector is true (=1).

@node sysstructtf
@subsection @code{tf} format variables

@table @var
@item num
 numerator coefficients   (vector)

@item den
 denominator coefficients   (vector)

@end table

@node sysstructzp
@subsection @code{zp} format variables

@table @var
@item zer
 system zeros   (vector)

@item pol
 system poles    (vector)

@item k
 leading coefficient   (scalar)

@end table

@node sysstructss
@subsection @code{ss} format variables

@table @var
@item a
@itemx b
@itemx c
@itemx d
The usual state-space matrices. If a system has both
        continuous and discrete states, they are sorted so that
        continuous states come first, then discrete states

@strong{Note} some functions (e.g., @code{bode}, @code{hinfsyn}) 
will not accept systems with both discrete and continuous states/outputs

@item stname
names of system states   (list of strings)

@end table

@node sysinterface
@section System Construction and Interface Functions

Construction and manipulations of the @acronym{OCST} system data structure
(@pxref{sysstruct}) requires attention to many details in order
to ensure that data structure contents remain consistent.  Users
are strongly encouraged to use the system interface functions
in this section.  Functions for the formatted display in of system
data structures are given in @ref{sysdisp}.

@menu
* fir2sys::                     
* ss2sys::                      
* tf2sys::                      
* zp2sys::                      
* structaccess::                
@end menu

@node fir2sys
@subsection Finite impulse response system interface functions

@anchor{doc-fir2sys}
@deftypefn {Function File} {} fir2sys (@var{num}, @var{tsam}, @var{inname}, @var{outname})
construct a system data structure from @acronym{FIR} description

@strong{Inputs}
@table @var
@item num
vector of coefficients 
@ifinfo
[c0, c1, @dots{}, cn]
@end ifinfo
@iftex
@tex
$ [c_0, c_1, \ldots, c_n ]$
@end tex
@end iftex
of the @acronym{SISO} @acronym{FIR} transfer function
@ifinfo
C(z) = c0 + c1*z^(-1) + c2*z^(-2) + @dots{} + cn*z^(-n)
@end ifinfo
@iftex
@tex
$$ C(z) = c_0 + c_1z^{-1} + c_2z^{-2} + \ldots + c_nz^{-n} $$
@end tex
@end iftex

@item tsam
sampling time (default: 1)

@item inname
name of input signal;  may be a string or a list with a single entry.

@item outname
name of output signal; may be a string or a list with a single entry.
@end table

@strong{Output}
@table @var
@item sys
system data structure
@end table

@strong{Example}
@example
octave:1> sys = fir2sys([1 -1 2 4],0.342,\
> "A/D input","filter output");
octave:2> sysout(sys)
Input(s)
        1: A/D input

Output(s):
        1: filter output (discrete)

Sampling interval: 0.342
transfer function form:
1*z^3 - 1*z^2 + 2*z^1 + 4
-------------------------
1*z^3 + 0*z^2 + 0*z^1 + 0
@end example
@end deftypefn


@anchor{doc-sys2fir}
@deftypefn {Function File} {[@var{c}, @var{tsam}, @var{input}, @var{output}] =} sys2fir (@var{sys})

Extract @acronym{FIR} data from system data structure; see @command{fir2sys} for
parameter descriptions.
@seealso{fir2sys}
@end deftypefn


@node ss2sys
@subsection State space system interface functions

@anchor{doc-ss}
@deftypefn {Function File} {@var{outsys} =} ss (@var{a}, @var{b}, @var{c}, @var{d}, @var{tsam}, @var{n}, @var{nz}, @var{stname}, @var{inname}, @var{outname}, @var{outlist})
Create system structure from state-space data.   May be continuous,
discrete, or mixed (sampled data)

@strong{Inputs}
@table @var
@item a
@itemx b
@itemx c
@itemx d
usual state space matrices.

default: @var{d} = zero matrix

@item   tsam
sampling rate.  Default: @math{tsam = 0} (continuous system)

@item n
@itemx nz
number of continuous, discrete states in the system

If @var{tsam} is 0, @math{n = @code{rows}(@var{a})}, @math{nz = 0}.

If @var{tsam} is greater than zero, @math{n = 0},
@math{nz = @code{rows}(@var{a})}

see below for system partitioning

@item  stname
cell array of strings of state signal names

default (@var{stname}=[] on input): @code{x_n} for continuous states,
@code{xd_n} for discrete states

@item inname
cell array of strings of input signal names

default (@var{inname} = [] on input): @code{u_n}

@item outname
cell array of strings of output signal names

default (@var{outname} = [] on input): @code{y_n}

@item   outlist

list of indices of outputs y that are sampled

If @var{tsam} is 0, @math{outlist = []}.

If @var{tsam} is greater than 0, @math{outlist = 1:@code{rows}(@var{c})}.
@end table

Unlike states, discrete/continuous outputs may appear in any order.

@code{sys2ss} returns a vector @var{yd} where
@var{yd}(@var{outlist}) = 1; all other entries of @var{yd} are 0.

@strong{Output}
@table @var
@item outsys
system data structure
@end table

@strong{System partitioning}

Suppose for simplicity that outlist specified
that the first several outputs were continuous and the remaining outputs
were discrete.  Then the system is partitioned as
@example
@group
x = [ xc ]  (n x 1)
    [ xd ]  (nz x 1 discrete states)
a = [ acc acd ]  b = [ bc ]
    [ adc add ]      [ bd ]
c = [ ccc ccd ]  d = [ dc ]
    [ cdc cdd ]      [ dd ]

    (cdc = c(outlist,1:n), etc.)
@end group
@end example
with dynamic equations:
@ifinfo
@math{d/dt xc(t)     = acc*xc(t)      + acd*xd(k*tsam) + bc*u(t)}

@math{xd((k+1)*tsam) = adc*xc(k*tsam) + add*xd(k*tsam) + bd*u(k*tsam)}

@math{yc(t)      = ccc*xc(t)      + ccd*xd(k*tsam) + dc*u(t)}

@math{yd(k*tsam) = cdc*xc(k*tsam) + cdd*xd(k*tsam) + dd*u(k*tsam)}
@end ifinfo
@iftex
@tex
$$\eqalign{
{d \over dt} x_c(t)
  & =   a_{cc} x_c(t)      + a_{cd} x_d(k*t_{sam}) + bc*u(t) \cr
x_d((k+1)*t_{sam})
  & =   a_{dc} x_c(k t_{sam}) + a_{dd} x_d(k t_{sam}) + b_d u(k t_{sam}) \cr
y_c(t)
 & =  c_{cc} x_c(t) + c_{cd} x_d(k t_{sam}) + d_c u(t) \cr
y_d(k t_{sam})
  & =  c_{dc} x_c(k t_{sam}) + c_{dd} x_d(k t_{sam}) + d_d u(k t_{sam})
}$$
@end tex
@end iftex

@strong{Signal partitions}
@example
@group
        | continuous      | discrete               |
----------------------------------------------------
states  | stname(1:n,:)   | stname((n+1):(n+nz),:) |
----------------------------------------------------
outputs | outname(cout,:) | outname(outlist,:)     |
----------------------------------------------------
@end group
@end example
where @math{cout} is the list of in 1:@code{rows}(@var{p})
that are not contained in outlist. (Discrete/continuous outputs
may be entered in any order desired by the user.)

@strong{Example}
@example
octave:1> a = [1 2 3; 4 5 6; 7 8 10];
octave:2> b = [0 0 ; 0 1 ; 1 0];
octave:3> c = eye (3);
octave:4> sys = ss (a, b, c, [], 0, 3, 0, ...
>                   @{"volts", "amps", "joules"@});
octave:5> sysout(sys);
Input(s)
        1: u_1
        2: u_2

Output(s):
        1: y_1
        2: y_2
        3: y_3

state-space form:
3 continuous states, 0 discrete states
State(s):
        1: volts
        2: amps
        3: joules

A matrix: 3 x 3
   1   2   3
   4   5   6
   7   8  10
B matrix: 3 x 2
  0  0
  0  1
  1  0
C matrix: 3 x 3
  1  0  0
  0  1  0
  0  0  1
D matrix: 3 x 3
  0  0
  0  0
  0  0
@end example
Notice that the @math{D} matrix is constructed  by default to the
correct dimensions.  Default input and output signals names were assigned
since none were given.
@end deftypefn


@anchor{doc-ss2sys}
@deftypefn {Function File} {} ss2sys (@var{a}, @var{b}, @var{c}, @var{d}, @var{tsam}, @var{n}, @var{nz}, @var{stname}, @var{inname}, @var{outname}, @var{outlist})
Create system structure from state-space data.   May be continuous,
discrete, or mixed (sampled data)

@strong{Inputs}
@table @var
@item a
@itemx b
@itemx c
@itemx d
usual state space matrices.

default: @var{d} = zero matrix

@item   tsam
sampling rate.  Default: @math{tsam = 0} (continuous system)

@item n
@itemx nz
number of continuous, discrete states in the system

If @var{tsam} is 0, @math{n = @code{rows}(@var{a})}, @math{nz = 0}.

If @var{tsam} is greater than zero, @math{n = 0},
@math{nz = @code{rows}(@var{a})}

see below for system partitioning

@item  stname
cell array of strings of state signal names

default (@var{stname}=[] on input): @code{x_n} for continuous states,
@code{xd_n} for discrete states

@item inname
cell array of strings of input signal names

default (@var{inname} = [] on input): @code{u_n}

@item outname
cell array of strings of input signal names

default (@var{outname} = [] on input): @code{y_n}

@item   outlist

list of indices of outputs y that are sampled

If @var{tsam} is 0, @math{outlist = []}.

If @var{tsam} is greater than 0, @math{outlist = 1:@code{rows}(@var{c})}.
@end table

Unlike states, discrete/continuous outputs may appear in any order.

@code{sys2ss} returns a vector @var{yd} where
@var{yd}(@var{outlist}) = 1; all other entries of @var{yd} are 0.

@strong{Outputs}
@var{outsys} = system data structure

@strong{System partitioning}

Suppose for simplicity that outlist specified
that the first several outputs were continuous and the remaining outputs
were discrete.  Then the system is partitioned as
@example
@group
x = [ xc ]  (n x 1)
    [ xd ]  (nz x 1 discrete states)
a = [ acc acd ]  b = [ bc ]
    [ adc add ]      [ bd ]
c = [ ccc ccd ]  d = [ dc ]
    [ cdc cdd ]      [ dd ]

    (cdc = c(outlist,1:n), etc.)
@end group
@end example
with dynamic equations:
@ifinfo
@math{d/dt xc(t)     = acc*xc(t)      + acd*xd(k*tsam) + bc*u(t)}

@math{xd((k+1)*tsam) = adc*xc(k*tsam) + add*xd(k*tsam) + bd*u(k*tsam)}

@math{yc(t)      = ccc*xc(t)      + ccd*xd(k*tsam) + dc*u(t)}

@math{yd(k*tsam) = cdc*xc(k*tsam) + cdd*xd(k*tsam) + dd*u(k*tsam)}
@end ifinfo
@iftex
@tex
$$\eqalign{
{d \over dt} x_c(t)
  & =   a_{cc} x_c(t)      + a_{cd} x_d(k*t_{sam}) + bc*u(t) \cr
x_d((k+1)*t_{sam})
  & =   a_{dc} x_c(k t_{sam}) + a_{dd} x_d(k t_{sam}) + b_d u(k t_{sam}) \cr
y_c(t)
 & =  c_{cc} x_c(t) + c_{cd} x_d(k t_{sam}) + d_c u(t) \cr
y_d(k t_{sam})
  & =  c_{dc} x_c(k t_{sam}) + c_{dd} x_d(k t_{sam}) + d_d u(k t_{sam})
}$$
@end tex
@end iftex

@strong{Signal partitions}
@example
@group
        | continuous      | discrete               |
----------------------------------------------------
states  | stname(1:n,:)   | stname((n+1):(n+nz),:) |
----------------------------------------------------
outputs | outname(cout,:) | outname(outlist,:)     |
----------------------------------------------------
@end group
@end example
where @math{cout} is the list of in 1:@code{rows}(@var{p})
that are not contained in outlist. (Discrete/continuous outputs
may be entered in any order desired by the user.)

@strong{Example}
@example
octave:1> a = [1 2 3; 4 5 6; 7 8 10];
octave:2> b = [0 0 ; 0 1 ; 1 0];
octave:3> c = eye (3);
octave:4> sys = ss (a, b, c, [], 0, 3, 0, 
>                   @{"volts", "amps", "joules"@});
octave:5> sysout(sys);
Input(s)
        1: u_1
        2: u_2

Output(s):
        1: y_1
        2: y_2
        3: y_3

state-space form:
3 continuous states, 0 discrete states
State(s):
        1: volts
        2: amps
        3: joules

A matrix: 3 x 3
   1   2   3
   4   5   6
   7   8  10
B matrix: 3 x 2
  0  0
  0  1
  1  0
C matrix: 3 x 3
  1  0  0
  0  1  0
  0  0  1
D matrix: 3 x 3
  0  0
  0  0
  0  0
@end example
Notice that the @math{D} matrix is constructed  by default to the
correct dimensions.  Default input and output signals names were assigned
since none were given.
@end deftypefn


@anchor{doc-sys2ss}
@deftypefn {Function File} {[@var{a}, @var{b}, @var{c}, @var{d}, @var{tsam}, @var{n}, @var{nz}, @var{stname}, @var{inname}, @var{outname}, @var{yd}] =} sys2ss (@var{sys})
Extract state space representation from system data structure.

@strong{Input}
@table @var
@item sys
System data structure.
@end table

@strong{Outputs}
@table @var
@item a
@itemx b
@itemx c
@itemx d
State space matrices for @var{sys}.

@item tsam
Sampling time of @var{sys} (0 if continuous).

@item n
@itemx nz
Number of continuous, discrete states (discrete states come
last in state vector @var{x}).

@item stname
@itemx inname
@itemx outname
Signal names (lists of strings);  names of states,
inputs, and outputs, respectively.

@item yd
Binary vector; @var{yd}(@var{ii}) is 1 if output @var{y}(@var{ii})
is discrete (sampled); otherwise  @var{yd}(@var{ii}) is 0.

@end table
A warning massage is printed if the system is a mixed
continuous and discrete system.

@strong{Example}
@example
octave:1> sys=tf2sys([1 2],[3 4 5]);
octave:2> [a,b,c,d] = sys2ss(sys)
a =
   0.00000   1.00000
  -1.66667  -1.33333
b =
  0
  1
c = 0.66667  0.33333
d = 0
@end example
@end deftypefn


@node tf2sys
@subsection Transfer function system interface functions

@anchor{doc-tf}
@deftypefn {Function File} {} tf (@var{num}, @var{den}, @var{tsam}, @var{inname}, @var{outname})
build system data structure from transfer function format data

@strong{Inputs}
@table @var
@item  num
@itemx den
coefficients of numerator/denominator polynomials
@item tsam
sampling interval. default: 0 (continuous time)
@item inname
@itemx outname
input/output signal names; may be a string or cell array with a single string
entry.
@end table

@strong{Outputs}
@var{sys} = system data structure

@strong{Example}
@example
octave:1> sys=tf([2 1],[1 2 1],0.1);
octave:2> sysout(sys)
Input(s)
        1: u_1
Output(s):
        1: y_1 (discrete)
Sampling interval: 0.1
transfer function form:
2*z^1 + 1
-----------------
1*z^2 + 2*z^1 + 1
@end example
@end deftypefn


@anchor{doc-tf2sys}
@deftypefn {Function File} {} tf2sys (@var{num}, @var{den}, @var{tsam}, @var{inname}, @var{outname})
Build system data structure from transfer function format data.

@strong{Inputs}
@table @var
@item  num
@itemx den
Coefficients of numerator/denominator polynomials.
@item tsam
Sampling interval; default: 0 (continuous time).
@item inname
@itemx outname
Input/output signal names; may be a string or cell array with a single string
entry.
@end table

@strong{Output}
@table @var
@item sys
System data structure.
@end table

@strong{Example}
@example
octave:1> sys=tf2sys([2 1],[1 2 1],0.1);
octave:2> sysout(sys)
Input(s)
        1: u_1
Output(s):
        1: y_1 (discrete)
Sampling interval: 0.1
transfer function form:
2*z^1 + 1
-----------------
1*z^2 + 2*z^1 + 1
@end example
@end deftypefn


@anchor{doc-sys2tf}
@deftypefn {Function File} {[@var{num}, @var{den}, @var{tsam}, @var{inname}, @var{outname}] =} sys2tf (@var{sys})
Extract transfer function data from a system data structure.

See @command{tf} for parameter descriptions.

@strong{Example}
@example
octave:1> sys=ss([1 -2; -1.1,-2.1],[0;1],[1 1]);
octave:2> [num,den] = sys2tf(sys)
num = 1.0000  -3.0000
den = 1.0000   1.1000  -4.3000
@end example
@end deftypefn


@node zp2sys
@subsection Zero-pole system interface functions

@anchor{doc-zp}
@deftypefn {Function File} {} zp (@var{zer}, @var{pol}, @var{k}, @var{tsam}, @var{inname}, @var{outname})
Create system data structure from zero-pole data.

@strong{Inputs}
@table @var
@item   zer
vector of system zeros
@item   pol
vector of system poles
@item   k
scalar leading coefficient
@item   tsam
sampling period. default: 0 (continuous system)
@item   inname
@itemx  outname
input/output signal names (lists of strings)
@end table

@strong{Outputs}
sys: system data structure

@strong{Example}
@example
octave:1> sys=zp([1 -1],[-2 -2 0],1);
octave:2> sysout(sys)
Input(s)
        1: u_1
Output(s):
        1: y_1
zero-pole form:
1 (s - 1) (s + 1)
-----------------
s (s + 2) (s + 2)
@end example
@end deftypefn


@anchor{doc-zp2sys}
@deftypefn {Function File} {} zp2sys (@var{zer}, @var{pol}, @var{k}, @var{tsam}, @var{inname}, @var{outname})
Create system data structure from zero-pole data.

@strong{Inputs}
@table @var
@item   zer
Vector of system zeros.
@item   pol
Vector of system poles.
@item   k
Scalar leading coefficient.
@item   tsam
Sampling period; default: 0 (continuous system).
@item   inname
@itemx  outname
Input/output signal names (lists of strings).
@end table

@strong{Output}
@table @var
@item sys
System data structure.
@end table

@strong{Example}
@example
octave:1> sys=zp2sys([1 -1],[-2 -2 0],1);
octave:2> sysout(sys)
Input(s)
        1: u_1
Output(s):
        1: y_1
zero-pole form:
1 (s - 1) (s + 1)
-----------------
s (s + 2) (s + 2)
@end example
@end deftypefn


@anchor{doc-sys2zp}
@deftypefn {Function File} {[@var{zer}, @var{pol}, @var{k}, @var{tsam}, @var{inname}, @var{outname}] =} sys2zp (@var{sys})
Extract zero/pole/leading coefficient information from a system data
structure.

See @command{zp} for parameter descriptions.

@strong{Example}
@example
octave:1> sys=ss([1 -2; -1.1,-2.1],[0;1],[1 1]);
octave:2> [zer,pol,k] = sys2zp(sys)
zer = 3.0000
pol =
  -2.6953
   1.5953
k = 1
@end example
@end deftypefn


@node structaccess
@subsection Data structure access functions

@anchor{doc-syschnames}
@deftypefn {Function File} {} syschnames (@var{sys}, @var{opt}, @var{list}, @var{names})
Superseded by @command{syssetsignals}.
@end deftypefn


@anchor{doc-syschtsam}
@deftypefn {Function File} {} syschtsam (@var{sys}, @var{tsam})
This function changes the sampling time (tsam) of the system.  Exits with
an error if sys is purely continuous time.
@end deftypefn


@anchor{doc-sysdimensions}
@deftypefn {Function File} {[@var{n}, @var{nz}, @var{m}, @var{p}, @var{yd}] =} sysdimensions (@var{sys}, @var{opt})
return the number of states, inputs, and/or outputs in the system
@var{sys}.

@strong{Inputs}
@table @var
@item sys
system data structure

@item opt
String indicating which dimensions are desired.  Values:
@table @code
@item "all"
(default) return all parameters as specified under Outputs below.

@item "cst"
return @var{n}= number of continuous states

@item "dst"
return @var{n}= number of discrete states

@item "in"
return @var{n}= number of inputs

@item "out"
return @var{n}= number of outputs
@end table
@end table

@strong{Outputs}
@table @var
@item  n
 number of continuous states (or individual requested dimension as specified
by @var{opt}).
@item  nz
 number of discrete states
@item  m
 number of system inputs
@item  p
 number of system outputs
@item  yd
 binary vector; @var{yd}(@var{ii}) is nonzero if output @var{ii} is
discrete.
@math{yd(ii) = 0} if output @var{ii} is continuous
@end table
@seealso{sysgetsignals, sysgettsam}
@end deftypefn


@anchor{doc-sysgetsignals}
@deftypefn {Function File} {[@var{stname}, @var{inname}, @var{outname}, @var{yd}] =} sysgetsignals (@var{sys})
@deftypefnx {Function File} {@var{siglist} =} sysgetsignals (@var{sys}, @var{sigid})
@deftypefnx {Function File} {@var{signame} =} sysgetsignals (@var{sys}, @var{sigid}, @var{signum}, @var{strflg})
Get signal names from a system

@strong{Inputs}
@table @var
@item sys
system data structure for the state space system

@item sigid
signal id.  String.  Must be one of
@table @code
@item "in"
input signals
@item "out"
output signals
@item "st"
stage signals
@item "yd"
value of logical vector @var{yd}
@end table

@item signum
index(indices) or name(s) or signals; see @code{sysidx}

@item strflg
flag to return a string instead of a cell array;  Values:
@table @code
@item 0
(default) return a cell array (even if signum specifies an individual signal)

@item 1
return a string.  Exits with an error if signum does not specify an 
individual signal.
@end table

@end table

@strong{Outputs}
@table @bullet
@item If @var{sigid} is not specified:
@table @var
@item stname
@itemx inname
@itemx outname
signal names (cell array of strings);  names of states,
inputs, and outputs, respectively.
@item yd
binary vector; @var{yd}(@var{ii}) is nonzero if output @var{ii} is
discrete.
@end table

@item If @var{sigid} is specified but @var{signum} is not specified:
@table @code
@item sigid="in"
@var{siglist} is set to the cell array of input names.

@item sigid="out"
@var{siglist} is set to the cell array of output names.

@item sigid="st"
@var{siglist} is set to the cell array of state names.

stage signals
@item sigid="yd"
@var{siglist} is set to logical vector indicating discrete outputs;
@var{siglist}(@var{ii}) = 0 indicates that output @var{ii} is continuous
(unsampled), otherwise it is discrete.

@end table

@item If the first three input arguments are specified:
@var{signame} is a cell array of the specified signal names (@var{sigid} is 
@code{"in"}, @code{"out"}, or @code{"st"}), or else the logical flag
indicating whether output(s) @var{signum} is(are) discrete (@var{sigval}=1)
or continuous (@var{sigval}=0).
@end table

@strong{Examples} (From @code{sysrepdemo})
@example
octave> sys=ss(rand(4),rand(4,2),rand(3,4));
octave># get all signal names
octave> [Ast,Ain,Aout,Ayd] = sysgetsignals(sys)
Ast =
(
  [1] = x_1
  [2] = x_2
  [3] = x_3
  [4] = x_4
)
Ain =
(
  [1] = u_1
  [2] = u_2
)
Aout =
(
  [1] = y_1
  [2] = y_2
  [3] = y_3
)
Ayd =

  0  0  0
octave> # get only input signal names:
octave> Ain = sysgetsignals(sys,"in")
Ain =
(
  [1] = u_1
  [2] = u_2
)
octave> # get name of output 2 (in cell array):
octave> Aout = sysgetsignals(sys,"out",2)
Aout =
(
  [1] = y_2
)
octave> # get name of output 2 (as string):
octave> Aout = sysgetsignals(sys,"out",2,1)
Aout = y_2
@end example
@end deftypefn


@anchor{doc-sysgettype}
@deftypefn {Function File} {} sysgettype (@var{sys})
return the initial system type of the system

@strong{Input}
@table @var
@item sys
System data structure.
@end table

@strong{Output}
@table @var
@item systype
String indicating how the structure was initially
constructed. Values: @code{"ss"}, @code{"zp"}, or @code{"tf"}.
@end table

@acronym{FIR} initialized systems return @code{systype="tf"}.
@end deftypefn


@anchor{doc-syssetsignals}
@deftypefn {Function File} {} syssetsignals (@var{sys}, @var{opt}, @var{names}, @var{sig_idx})
change the names of selected inputs, outputs and states.

@strong{Inputs}
@table @var
@item sys
System data structure.

@item opt
Change default name (output).

@table @code
@item "out"
Change selected output names.
@item "in"
Change selected input names.
@item "st"
Change selected state names.
@item "yd"
Change selected outputs from discrete to continuous or
from continuous to discrete.
@end table

@item names
@table @code
@item opt = "out", "in", "st"
string or string array containing desired signal names or values.
@item opt = "yd"
To desired output continuous/discrete flag.
Set name to 0 for continuous, or 1 for discrete.
@end table
@item sig_idx
indices or names of outputs, yd, inputs, or
states whose respective names/values should be changed.

Default: replace entire cell array of names/entire yd vector.
@end table

@strong{Outputs}
@table @var
@item retsys
@var{sys} with appropriate signal names changed
(or @var{yd} values, where appropriate).
@end table

@strong{Example}
@example
octave:1> sys=ss ([1 2; 3 4],[5;6],[7 8]);
octave:2> sys = syssetsignals (sys, "st",
>                              str2mat("Posx","Velx"));
octave:3> sysout(sys)
Input(s)
        1: u_1
Output(s):
        1: y_1
state-space form:
2 continuous states, 0 discrete states
State(s):
        1: Posx
        2: Velx
A matrix: 2 x 2
  1  2
  3  4
B matrix: 2 x 1
  5
  6
C matrix: 1 x 2
  7  8
D matrix: 1 x 1
0
@end example
@end deftypefn


@anchor{doc-sysupdate}
@deftypefn {Function File} {} sysupdate (@var{sys}, @var{opt})
Update the internal representation of a system.

@strong{Inputs}
@table @var
@item sys:
system data structure
@item opt
string:
@table @code
@item "tf"
update transfer function form
@item "zp"
update zero-pole form
@item "ss"
update state space form
@item "all"
all of the above
@end table
@end table

@strong{Outputs}
@table @var
@item retsys
Contains union of data in sys and requested data.
If requested data in @var{sys} is already up to date then @var{retsys}=@var{sys}.
@end table

Conversion to @command{tf} or @command{zp} exits with an error if the system is
mixed continuous/digital.
@seealso{tf, ss, zp, sysout, sys2ss, sys2tf, sys2zp}
@end deftypefn


@anchor{doc-minfo}
@deftypefn {Function File} {[@var{systype}, @var{nout}, @var{nin}, @var{ncstates}, @var{ndstates}] =} minfo (@var{inmat})
Determines the type of system matrix.  @var{inmat} can be a varying, 
a system, a constant, and an empty matrix.

@strong{Outputs}
@table @var
@item systype 
Can be one of: varying, system, constant, and empty.
@item nout 
The number of outputs of the system.
@item nin
The number of inputs of the system.
@item ncstates
The number of continuous states of the system.
@item ndstates 
The number of discrete states of the system.
@end table
@end deftypefn


@anchor{doc-sysgettsam}
@deftypefn {Function File} {} sysgettsam (@var{sys})
Return the sampling time of the system @var{sys}.
@end deftypefn


@node sysdisp
@section System display functions

@anchor{doc-sysout}
@deftypefn {Function File} {} sysout (@var{sys}, @var{opt})
print out a system data structure in desired format
@table @var
@item  sys
system data structure
@item  opt
Display option
@table @code
@item []
primary system form (default)
@item      "ss"
state space form
@item      "tf"
transfer function form
@item      "zp"
zero-pole form
@item      "all"
all of the above
@end table
@end table
@end deftypefn


@anchor{doc-tfout}
@deftypefn {Function File} {} tfout (@var{num}, @var{denom}, @var{x})
Print formatted transfer function @math{n(s)/d(s)} to the screen.
@var{x} defaults to the string @code{"s"}
@seealso{polyval, polyvalm, poly, roots, conv, deconv, residue,
filter, polyderiv, polyinteg, polyout}
@end deftypefn


@anchor{doc-zpout}
@deftypefn {Function File} {} zpout (@var{zer}, @var{pol}, @var{k}, @var{x})
print formatted zero-pole form to the screen.
@var{x} defaults to the string @code{"s"}
@seealso{polyval, polyvalm, poly, roots, conv, deconv, residue,
filter, polyderiv, polyinteg, polyout}
@end deftypefn


@node blockdiag
@section Block Diagram Manipulations

@xref{systime}.

Unless otherwise noted, all parameters (input,output) are
system data structures.

@anchor{doc-bddemo}
@deftypefn {Function File} {} bddemo (@var{inputs})
Octave Controls toolbox demo: Block Diagram Manipulations demo.
@end deftypefn


@anchor{doc-buildssic}
@deftypefn {Function File} {} buildssic (@var{clst}, @var{ulst}, @var{olst}, @var{ilst}, @var{s1}, @var{s2}, @var{s3}, @var{s4}, @var{s5}, @var{s6}, @var{s7}, @var{s8})

Form an arbitrary complex (open or closed loop) system in
state-space form from several systems. @command{buildssic} can
easily (despite its cryptic syntax) integrate transfer functions
from a complex block diagram into a single system with one call.
This function is especially useful for building open loop
interconnections for 
@iftex
@tex
$ { \cal H }_\infty $ and $ { \cal H }_2 $
@end tex
@end iftex
@ifinfo
H-infinity and H-2
@end ifinfo
designs or for closing loops with these controllers.

Although this function is general purpose, the use of @command{sysgroup}
@command{sysmult}, @command{sysconnect} and the like is recommended for
standard operations since they can handle mixed discrete and continuous
systems and also the names of inputs, outputs, and states.

The parameters consist of 4 lists that describe the connections
outputs and inputs and up to 8 systems @var{s1}--@var{s8}.
Format of the lists:
@table @var
@item      clst
connection list, describes the input signal of
each system. The maximum number of rows of Clst is
equal to the sum of all inputs of s1-s8.

Example:
@code{[1 2 -1; 2 1 0]} means that:  new input 1 is old input 1
+ output 2 - output 1, and new input 2 is old input 2
+ output 1. The order of rows is arbitrary.

@item ulst
if not empty the old inputs in vector @var{ulst} will
be appended to the outputs. You need this if you
want to ``pull out'' the input of a system. Elements
are input numbers of @var{s1}--@var{s8}.

@item olst
output list, specifies the outputs of the resulting
systems. Elements are output numbers of @var{s1}--@var{s8}.
The numbers are allowed to be negative and may
appear in any order. An empty matrix means
all outputs.

@item ilst
input list, specifies the inputs of the resulting
systems. Elements are input numbers of @var{s1}--@var{s8}.
The numbers are allowed to be negative and may
appear in any order. An empty matrix means
all inputs.
@end table

Example:  Very simple closed loop system.
@example
@group
w        e  +-----+   u  +-----+
 --->o--*-->|  K  |--*-->|  G  |--*---> y
     ^  |   +-----+  |   +-----+  |
   - |  |            |            |
     |  |            +----------------> u
     |  |                         |
     |  +-------------------------|---> e
     |                            |
     +----------------------------+
@end group
@end example

The closed loop system @var{GW} can be obtained by
@example
GW = buildssic([1 2; 2 -1], 2, [1 2 3], 2, G, K);
@end example
@table @var
@item clst
1st row: connect input 1 (@var{G}) with output 2 (@var{K}).

2nd row: connect input 2 (@var{K}) with negative output 1 (@var{G}).
@item ulst
Append input of 2 (@var{K}) to the number of outputs.
@item olst
Outputs are output of 1 (@var{G}), 2 (@var{K}) and 
appended output 3 (from @var{ulst}).
@item ilst
The only input is 2 (@var{K}).
@end table

Here is a real example:
@example
@group
                         +----+
    -------------------->| W1 |---> v1
z   |                    +----+
----|-------------+
    |             |
    |    +---+    v      +----+
    *--->| G |--->O--*-->| W2 |---> v2
    |    +---+       |   +----+
    |                |
    |                v
   u                  y
@end group
@end example
@iftex
@tex
$$ { \rm min } \Vert GW_{vz} \Vert _\infty $$  
@end tex
@end iftex
@ifinfo
@example
min || GW   ||
         vz   infty
@end example
@end ifinfo

The closed loop system @var{GW} 
@iftex
@tex
from $ [z, u]^T $ to $ [v_1, v_2, y]^T $
@end tex
@end iftex
@ifinfo
from [z, u]' to [v1, v2, y]' 
@end ifinfo
can be obtained by (all @acronym{SISO} systems):
@example
GW = buildssic([1, 4; 2, 4; 3, 1], 3, [2, 3, 5],
               [3, 4], G, W1, W2, One);
@end example
where ``One'' is a unity gain (auxiliary) function with order 0.
(e.g. @code{One = ugain(1);})
@end deftypefn


@anchor{doc-jet707}
@deftypefn {Function File} {@var{sys} =} jet707 ()
Creates a linearized state-space model of a Boeing 707-321 aircraft
at @var{v}=80 m/s 
@iftex
@tex
($M = 0.26$, $G_{a0} = -3^{\circ}$, ${\alpha}_0 = 4^{\circ}$, ${\kappa}= 50^{\circ}$).
@end tex
@end iftex
@ifinfo
(@var{M} = 0.26, @var{Ga0} = -3 deg, @var{alpha0} = 4 deg, @var{kappa} = 50 deg).
@end ifinfo

System inputs: (1) thrust and (2) elevator angle.

System outputs:  (1) airspeed and (2) pitch angle.

@strong{Reference}: R. Brockhaus: @cite{Flugregelung} (Flight
Control), Springer, 1994.
@seealso{ord2}
@end deftypefn


@anchor{doc-ord2}
@deftypefn {Function File} {} ord2 (@var{nfreq}, @var{damp}, @var{gain})
Creates a continuous 2nd order system with parameters:

@strong{Inputs}
@table @var
@item nfreq
natural frequency [Hz]. (not in rad/s)
@item damp
damping coefficient
@item gain
dc-gain
This is steady state value only for damp > 0.
gain is assumed to be 1.0 if omitted.
@end table

@strong{Output}
@table @var
@item outsys
system data structure has representation with 
@ifinfo
@math{w = 2 * pi * nfreq}:
@end ifinfo
@iftex
@tex
$ w = 2  \pi  f $:
@end tex
@end iftex
@example
@group
    /                                        \
    | / -2w*damp -w \  / w \                 |
G = | |             |, |   |, [ 0  gain ], 0 |
    | \   w       0 /  \ 0 /                 |
    \                                        /
@end group
@end example
@end table
@strong{See also} @command{jet707} (@acronym{MIMO} example, Boeing 707-321
aircraft model)
@end deftypefn


@anchor{doc-sysadd}
@deftypefn {Function File} {}  sysadd (@var{gsys}, @var{hsys})
returns @var{sys} = @var{gsys} + @var{hsys}.
@itemize @bullet
@item Exits with
an error if @var{gsys} and @var{hsys} are not compatibly dimensioned.
@item Prints a warning message is system states have identical names;
duplicate names are given a suffix to make them unique.
@item @var{sys} input/output names are taken from @var{gsys}.
@end itemize
@example
@group
          ________
     ----|  gsys  |---
u   |    ----------  +|
-----                (_)----> y
    |     ________   +|
     ----|  hsys  |---
          --------
@end group
@end example
@end deftypefn


@anchor{doc-sysappend}
@deftypefn {Function File} {@var{sys} =} sysappend (@var{syst}, @var{b}, @var{c}, @var{d}, @var{outname}, @var{inname}, @var{yd})
appends new inputs and/or outputs to a system

@strong{Inputs}
@table @var
@item syst
system data structure

@item b
matrix to be appended to sys "B" matrix (empty if none)

@item c
matrix to be appended to sys "C" matrix (empty if none)

@item d
revised sys d matrix (can be passed as [] if the revised d is all zeros)

@item outname
list of names for new outputs

@item inname
list of names for new inputs

@item yd
binary vector; @math{yd(ii)=0} indicates a continuous output;
@math{yd(ii)=1} indicates a discrete output.
@end table

@strong{Outputs}
@table @var
@item sys
@example
@group
   sys.b := [syst.b , b]
   sys.c := [syst.c  ]
            [ c     ]
   sys.d := [syst.d | D12 ]
            [ D21   | D22 ]
@end group
@end example
where @math{D12}, @math{D21}, and @math{D22} are the appropriate dimensioned
blocks of the input parameter @var{d}.
@itemize @bullet
@item The leading block @math{D11} of @var{d} is ignored.
@item If @var{inname} and @var{outname} are not given as arguments,
     the new inputs and outputs are be assigned default names.
@item @var{yd} is a binary vector of length rows(c) that indicates
     continuous/sampled outputs.  Default value for @var{yd} is:
@itemize @minus
@item @var{sys} is continuous or mixed
@var{yd} = @code{zeros(1,rows(c))}

@item @var{sys} is discrete
@var{yd} = @code{ones(1,rows(c))}
@end itemize
@end itemize
@end table
@end deftypefn


@anchor{doc-sysconnect}
@deftypefn {Function File} {@var{clsys} =} sysconnect (@var{sys}, @var{out_idx}, @var{in_idx}, @var{order}, @var{tol})
Close the loop from specified outputs to respective specified inputs

@strong{Inputs}
@table @var
@item   sys
System data structure.
@item   out_idx
@itemx  in_idx
Names or indices of signals to connect (see @code{sysidx}).
The output specified by @math{out_idx(ii)} is connected to the input
specified by @math{in_idx(ii)}.
@item   order
logical flag (default = 0)
@table @code
@item        0
Leave inputs and outputs in their original order.
@item        1
Permute inputs and outputs to the order shown in the diagram below.
@end table
@item     tol
Tolerance for singularities in algebraic loops, default: 200@code{eps}.
@end table

@strong{Outputs}
@table @var
@item clsys
Resulting closed loop system.
@end table

@strong{Method}

@code{sysconnect} internally permutes selected inputs, outputs as shown
below, closes the loop, and then permutes inputs and outputs back to their
original order
@example
@group
                 --------------------
 u_1       ----->|                  |----> y_1
                 |        sys       |
         old u_2 |                  |
u_2* ---->(+)--->|                  |----->y_2
(in_idx)   ^     --------------------    | (out_idx)
           |                             |
           -------------------------------
@end group
@end example
The input that has the summing junction added to it has an * added to
the end  of the input name.
@end deftypefn


@anchor{doc-syscont}
@deftypefn {Function File} {[@var{csys}, @var{acd}, @var{ccd}] =} syscont (@var{sys})
Extract the purely continuous subsystem of an input system.

@strong{Input}
@table @var
@item sys
system data structure.
@end table

@strong{Outputs}
@table @var
@item csys
is the purely continuous input/output connections of @var{sys}
@item acd
@itemx ccd
connections from discrete states to continuous states,
discrete states to continuous outputs, respectively.

If no continuous path exists, @var{csys} will be empty.
@end table
@end deftypefn


@anchor{doc-sysdisc}
@deftypefn {Function File} {[@var{dsys}, @var{adc}, @var{cdc}] =} sysdisc (@var{sys})

@strong{Input}
@table @var
@item sys
System data structure.
@end table

@strong{Outputs}
@table @var
@item dsys
Purely discrete portion of sys (returned empty if there is
no purely discrete path from inputs to outputs).
@item    adc
@itemx   cdc
Connections from continuous states to discrete states and discrete
outputs, respectively.
@end table
@end deftypefn


@anchor{doc-sysdup}
@deftypefn {Function File} {@var{retsys} =} sysdup (@var{asys}, @var{out_idx}, @var{in_idx})
Duplicate specified input/output connections of a system

@strong{Inputs}
@table @var
@item asys
system data structure
@item out_idx
@itemx in_idx
indices or names of desired signals (see @code{sigidx}).
duplicates are made of @code{y(out_idx(ii))} and @code{u(in_idx(ii))}.
@end table

@strong{Output}
@table @var
@item retsys
Resulting closed loop system:
duplicated i/o names are appended with a @code{"+"} suffix.
@end table

@strong{Method}

@code{sysdup} creates copies of selected inputs and outputs as
shown below.  @var{u1}, @var{y1} is the set of original inputs/outputs, and
@var{u2}, @var{y2} is the set of duplicated inputs/outputs in the order 
specified in @var{in_idx}, @var{out_idx}, respectively
@example
@group
          ____________________
u1  ----->|                  |----> y1
          |       asys       |
u2 ------>|                  |----->y2
(in_idx)  -------------------- (out_idx)
@end group
@end example
@end deftypefn
 

@anchor{doc-sysgroup}
@deftypefn {Function File} {@var{sys} =} sysgroup (@var{asys}, @var{bsys})
Combines two systems into a single system.

@strong{Inputs}
@table @var
@item asys
@itemx bsys
System data structures.
@end table

@strong{Output}
@table @var
@item sys
@math{sys = @r{block diag}(asys,bsys)}
@end table
@example
@group
         __________________
         |    ________    |
u1 ----->|--> | asys |--->|----> y1
         |    --------    |
         |    ________    |
u2 ----->|--> | bsys |--->|----> y2
         |    --------    |
         ------------------
              Ksys
@end group
@end example
The function also rearranges the internal state-space realization of @var{sys}
so that the continuous states come first and the discrete states come last.
If there are duplicate names, the second name has a unique suffix appended
on to the end of the name.
@end deftypefn


@anchor{doc-sysmult}
@deftypefn {Function File} {@var{sys} =} sysmult (@var{Asys}, @var{Bsys})
Compute @math{sys = Asys*Bsys} (series connection):
@example
@group
u   ----------     ----------
--->|  Bsys  |---->|  Asys  |--->
    ----------     ----------
@end group
@end example
A warning occurs if there is direct feed-through from an input 
or a continuous state of @var{Bsys}, through a discrete output 
of @var{Bsys}, to a continuous state or output in @var{Asys}
(system data structure does not recognize discrete inputs).
@end deftypefn


@anchor{doc-sysprune}
@deftypefn {Function File} {@var{retsys} =} sysprune (@var{asys}, @var{out_idx}, @var{in_idx})
Extract specified inputs/outputs from a system

@strong{Inputs}
@table @var
@item asys
system data structure
@item out_idx
@itemx in_idx
Indices or signal names of the outputs and inputs to be kept in the returned
system; remaining connections are ``pruned'' off.
May select as [] (empty matrix) to specify all outputs/inputs.

@example
retsys = sysprune (Asys, [1:3,4], "u_1");
retsys = sysprune (Asys, @{"tx", "ty", "tz"@}, 4);
@end example

@end table

@strong{Output}
@table @var
@item retsys
Resulting system.
@end table
@example
@group
           ____________________
u1 ------->|                  |----> y1
 (in_idx)  |       Asys       | (out_idx)
u2 ------->|                  |----| y2
  (deleted)-------------------- (deleted)
@end group
@end example
@end deftypefn


@anchor{doc-sysreorder}
@deftypefn {Function File} {@var{pv} =} sysreorder (@var{vlen}, @var{list})

@strong{Inputs}
@table @var
@item vlen
Vector length.
@item list
A subset of @code{[1:vlen]}.
@end table

@strong{Output}
@table @var
@item pv
A permutation vector to order elements of @code{[1:vlen]} in
@code{list} to the end of a vector.
@end table

Used internally by @code{sysconnect} to permute vector elements to their
desired locations.
@end deftypefn


@anchor{doc-sysscale}
@deftypefn {Function File} {@var{retsys} =} sysscale (@var{sys}, @var{outscale}, @var{inscale}, @var{outname}, @var{inname})
scale inputs/outputs of a system.

@strong{Inputs}
@table @var
@item sys
Structured system.
@item outscale
@itemx inscale
Constant matrices of appropriate dimension.
@item outname
@itemx inname
Lists of strings with the names of respectively outputs and inputs.
@end table

@strong{Output}
@table @var
@item retsys
resulting open loop system:
@smallexample
      -----------    -------    -----------
u --->| inscale |--->| sys |--->| outscale |---> y
      -----------    -------    -----------
@end smallexample
@end table
If the input names and output names (each a list of strings)
are not given and the scaling matrices
are not square, then default names will be given to the inputs and/or
outputs.

A warning message is printed if outscale attempts to add continuous
system outputs to discrete system outputs; otherwise @var{yd} is
set appropriately in the returned value of @var{sys}.
@end deftypefn


@anchor{doc-syssub}
@deftypefn {Function File} {@var{sys} =} syssub (@var{Gsys}, @var{Hsys})
Return @math{sys = Gsys - Hsys}.

@strong{Method}

@var{Gsys} and @var{Hsys} are connected in parallel.
The input vector is connected to both systems; the outputs are
subtracted.  Returned system names are those of @var{Gsys}.
@example
@group
         +--------+
    +--->|  Gsys  |---+
    |    +--------+   |
    |                +|
u --+                (_)--> y
    |                -|
    |    +--------+   |
    +--->|  Hsys  |---+
         +--------+
@end group
@end example
@end deftypefn


@anchor{doc-ugain}
@deftypefn {Function File} {} ugain (@var{n})
Creates a system with unity gain, no states.
This trivial system is sometimes needed to create arbitrary
complex systems from simple systems with @command{buildssic}.
Watch out if you are forming sampled systems since @command{ugain}
does not contain a sampling period.
@seealso{hinfdemo, jet707}
@end deftypefn


@anchor{doc-wgt1o}
@deftypefn {Function File} {@var{W} =} wgt1o (@var{vl}, @var{vh}, @var{fc})
State space description of a first order weighting function.

Weighting function are needed by the 
@iftex
@tex
$ { \cal H }_2 / { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-2/H-infinity
@end ifinfo
design procedure.
These functions are part of the augmented plant @var{P}
(see @command{hinfdemo} for an application example).

@strong{Inputs}
@table @var
@item vl
Gain at low frequencies.
@item vh
Gain at high frequencies.
@item fc
Corner frequency (in Hz, @strong{not} in rad/sec)
@end table

@strong{Output}
@table @var
@item W
Weighting function, given in form of a system data structure.
@end table
@end deftypefn


@anchor{doc-parallel}
@deftypefn {Function File} {@var{ksys} =} parallel (@var{asys}, @var{bsys})
Forms the parallel connection of two systems.

@example
@group
             --------------------
             |      --------    |
    u  ----->|----> | asys |--->|----> y1
        |    |      --------    |
        |    |      --------    |
        |--->|----> | bsys |--->|----> y2
             |      --------    |
             --------------------
                  ksys
@end group
@end example
@end deftypefn


@anchor{doc-sysmin}
@deftypefn {Function File} {[@var{retsys}, @var{nc}, @var{no}] =} sysmin (@var{sys}, @var{flg})
Returns a minimal (or reduced order) system

@strong{Inputs}
@table @var
@item sys
System data structure
@item flg
When equal to 0 (default value), returns minimal system,
in which state names are lost; when equal to 1, returns system 
with physical states removed that are either uncontrollable or 
unobservable (cannot reduce further without discarding physical
meaning of states).
@end table
@strong{Outputs}
@table @var
@item retsys
Returned system.
@item nc
Number of controllable states in the returned system.
@item no
Number of observable states in the returned system.
@item cflg
@code{is_controllable(retsys)}.
@item oflg
@code{is_observable(retsys)}.
@end table
@end deftypefn


@node numerical
@section Numerical Functions

@anchor{doc-are}
@deftypefn {Function File} {@var{x} =} are (@var{a}, @var{b}, @var{c}, @var{opt})
Solve the Algebraic Riccati Equation
@iftex
@tex
$$
A^TX + XA - XBX + C = 0
$$
@end tex
@end iftex
@ifinfo
@example
a' * x + x * a - x * b * x + c = 0
@end example
@end ifinfo

@strong{Inputs}
@noindent
for identically dimensioned square matrices
@table @var
@item a
@var{n} by @var{n} matrix;
@item b
@var{n} by @var{n} matrix or @var{n} by @var{m} matrix; in the latter case
@var{b} is replaced by @math{b:=b*b'};
@item c
@var{n} by @var{n} matrix or @var{p} by @var{m} matrix; in the latter case
@var{c} is replaced by @math{c:=c'*c};
@item opt
(optional argument; default = @code{"B"}):
String option passed to @code{balance} prior to ordered Schur decomposition.
@end table

@strong{Output}
@table @var
@item x
solution of the @acronym{ARE}.
@end table

@strong{Method}
Laub's Schur method (@acronym{IEEE} Transactions on
Automatic Control, 1979) is applied to the appropriate Hamiltonian
matrix.
@seealso{balance, dare}
@end deftypefn


@anchor{doc-dare}
@deftypefn {Function File} {@var{x} =} dare (@var{a}, @var{b}, @var{q}, @var{r}, @var{opt})

Return the solution, @var{x} of the discrete-time algebraic Riccati
equation
@iftex
@tex
$$
A^TXA - X + A^TXB  (R + B^TXB)^{-1} B^TXA + Q = 0
$$
@end tex
@end iftex
@ifinfo
@example
a' x a - x + a' x b (r + b' x b)^(-1) b' x a + q = 0
@end example
@end ifinfo
@noindent

@strong{Inputs}
@table @var
@item a
@var{n} by @var{n} matrix;

@item b
@var{n} by @var{m} matrix;

@item q
@var{n} by @var{n} matrix, symmetric positive semidefinite, or a @var{p} by @var{n} matrix,
In the latter case @math{q:=q'*q} is used;

@item r
@var{m} by @var{m}, symmetric positive definite (invertible);

@item opt
(optional argument; default = @code{"B"}):
String option passed to @code{balance} prior to ordered @var{QZ} decomposition.
@end table

@strong{Output}
@table @var
@item x
solution of @acronym{DARE}.
@end table

@strong{Method}
Generalized eigenvalue approach (Van Dooren; @acronym{SIAM} J.
 Sci. Stat. Comput., Vol 2) applied  to the appropriate symplectic pencil.

 See also: Ran and Rodman, @cite{Stable Hermitian Solutions of Discrete
 Algebraic Riccati Equations}, Mathematics of Control, Signals and
 Systems, Vol 5, no 2 (1992), pp 165--194.
@seealso{balance, are}
@end deftypefn


@anchor{doc-dre}
@deftypefn {Function File} {[@var{tvals}, @var{plist}] =} dre (@var{sys}, @var{q}, @var{r}, @var{qf}, @var{t0}, @var{tf}, @var{ptol}, @var{maxits})
Solve the differential Riccati equation
@ifinfo
@example
  -d P/dt = A'P + P A - P B inv(R) B' P + Q
  P(tf) = Qf
@end example
@end ifinfo
@iftex
@tex
$$ -{dP \over dt} = A^T P+PA-PBR^{-1}B^T P+Q $$
$$ P(t_f) = Q_f $$
@end tex
@end iftex
for the @acronym{LTI} system sys.  Solution of 
standard @acronym{LTI} state feedback optimization
@ifinfo
@example
  min int(t0, tf) ( x' Q x + u' R u ) dt + x(tf)' Qf x(tf)
@end example
@end ifinfo
@iftex
@tex
$$ \min \int_{t_0}^{t_f} x^T Q x + u^T R u dt + x(t_f)^T Q_f x(t_f) $$
@end tex
@end iftex
optimal input is
@ifinfo
@example
  u = - inv(R) B' P(t) x
@end example
@end ifinfo
@iftex
@tex
$$ u = - R^{-1} B^T P(t) x $$
@end tex
@end iftex
@strong{Inputs}
@table @var
@item sys
continuous time system data structure
@item q
state integral penalty
@item r
input integral penalty
@item qf
state terminal penalty
@item t0
@itemx tf
limits on the integral
@item ptol
tolerance (used to select time samples; see below); default = 0.1
@item maxits
number of refinement iterations (default=10)
@end table
@strong{Outputs}
@table @var
@item tvals
time values at which @var{p}(@var{t}) is computed
@item plist
list values of @var{p}(@var{t}); @var{plist} @{ @var{i} @}
is @var{p}(@var{tvals}(@var{i}))
@end table
@var{tvals} is selected so that:
@iftex
@tex
$$ \Vert plist_{i} - plist_{i-1} \Vert < ptol $$
@end tex
@end iftex
@ifinfo
@example
|| Plist@{i@} - Plist@{i-1@} || < Ptol
@end example
@end ifinfo
for every @var{i} between 2 and length(@var{tvals}).
@end deftypefn


@anchor{doc-dgram}
@deftypefn {Function File} {} dgram (@var{a}, @var{b})
Return controllability gramian of discrete time system
@iftex
@tex
$$ x_{k+1} = ax_k + bu_k $$
@end tex
@end iftex
@ifinfo
@example
  x(k+1) = a x(k) + b u(k)
@end example
@end ifinfo

@strong{Inputs}
@table @var
@item a
@var{n} by @var{n} matrix
@item b
@var{n} by @var{m} matrix
@end table

@strong{Output}
@table @var
@item m 
@var{n} by @var{n} matrix, satisfies
@iftex
@tex
$$ ama^T - m + bb^T = 0 $$
@end tex
@end iftex
@ifinfo
@example
 a m a' - m + b*b' = 0
@end example
@end ifinfo
@end table
@end deftypefn


@anchor{doc-dlyap}
@deftypefn {Function File} {} dlyap (@var{a}, @var{b})
Solve the discrete-time Lyapunov equation

@strong{Inputs}
@table @var
@item a
@var{n} by @var{n} matrix;
@item b
  Matrix: @var{n} by @var{n}, @var{n} by @var{m}, or @var{p} by @var{n}.
@end table

@strong{Output}
@table @var
@item x
matrix satisfying appropriate discrete time Lyapunov equation.
@end table

Options:
@itemize @bullet
@item @var{b} is square: solve 
@iftex
@tex
$$ axa^T - x + b = 0 $$
@end tex
@end iftex
@ifinfo
@code{a x a' - x + b = 0}
@end ifinfo
@item @var{b} is not square: @var{x} satisfies either
@iftex
@tex
$$ axa^T - x + bb^T = 0 $$
@end tex
@end iftex
@ifinfo
@example
a x a' - x + b b' = 0
@end example
@end ifinfo
@noindent
or
@iftex
@tex
$$ a^Txa - x + b^Tb = 0, $$
@end tex
@end iftex
@ifinfo
@example
a' x a - x + b' b = 0,
@end example
@end ifinfo
@noindent
whichever is appropriate.
@end itemize

@strong{Method}
Uses Schur decomposition method as in Kitagawa,
@cite{An Algorithm for Solving the Matrix Equation @math{X = F X F' + S}},
International Journal of Control, Volume 25, Number 5, pages 745--753
(1977).

Column-by-column solution method as suggested in
Hammarling, @cite{Numerical Solution of the Stable, Non-Negative
Definite Lyapunov Equation}, @acronym{IMA} Journal of Numerical Analysis, Volume
2, pages 303--323 (1982).
@end deftypefn


@anchor{doc-gram}
@deftypefn {Function File} {} gram (@var{a}, @var{b})
Return controllability gramian @var{m} of the continuous time system
@math{dx/dt = a x + b u}.

@var{m} satisfies @math{a m + m a' + b b' = 0}.
@end deftypefn


@anchor{doc-lyap}
@deftypefn {Function File} {} lyap (@var{a}, @var{b}, @var{c})
@deftypefnx {Function File} {} lyap (@var{a}, @var{b})
Solve the Lyapunov (or Sylvester) equation via the Bartels-Stewart
algorithm (Communications of the @acronym{ACM}, 1972).

If @var{a}, @var{b}, and @var{c} are specified, then @code{lyap} returns
the solution of the  Sylvester equation
@iftex
@tex
  $$ A X + X B + C = 0 $$
@end tex
@end iftex
@ifinfo
@example
    a x + x b + c = 0
@end example
@end ifinfo
If only @code{(a, b)} are specified, then @command{lyap} returns the
solution of the Lyapunov equation
@iftex
@tex
  $$ A^T X + X A + B = 0 $$
@end tex
@end iftex
@ifinfo
@example
    a' x + x a + b = 0
@end example
@end ifinfo
If @var{b} is not square, then @code{lyap} returns the solution of either
@iftex
@tex
  $$ A^T X + X A + B^T B = 0 $$
@end tex
@end iftex
@ifinfo
@example
    a' x + x a + b' b = 0
@end example
@end ifinfo
@noindent
or
@iftex
@tex
  $$ A X + X A^T + B B^T = 0 $$
@end tex
@end iftex
@ifinfo
@example
    a x + x a' + b b' = 0
@end example
@end ifinfo
@noindent
whichever is appropriate.

Solves by using the Bartels-Stewart algorithm (1972).
@end deftypefn


@anchor{doc-qzval}
@deftypefn {Function File} {} qzval (@var{a}, @var{b})
Compute generalized eigenvalues of the matrix pencil
@ifinfo
@example
(A - lambda B).
@end example
@end ifinfo
@iftex
@tex
$(A - \lambda B)$.
@end tex
@end iftex

@var{a} and @var{b} must be real matrices.

@code{qzval} is obsolete; use @code{qz} instead.
@end deftypefn


@anchor{doc-zgfmul}
@deftypefn {Function File} {@var{y} =} zgfmul (@var{a}, @var{b}, @var{c}, @var{d}, @var{x})
Compute product of @var{zgep} incidence matrix @math{F} with vector @var{x}.
Used by @command{zgepbal} (in @command{zgscal}) as part of generalized conjugate gradient
iteration.
@end deftypefn


@anchor{doc-zgfslv}
@deftypefn {Function File} {} zgfslv (@var{n}, @var{m}, @var{p}, @var{b})
Solve system of equations for dense zgep problem.
@end deftypefn


@anchor{doc-zginit}
@deftypefn {Function File} {@var{zz} =} zginit (@var{a}, @var{b}, @var{c}, @var{d})
Construct right hand side vector @var{zz}
for the zero-computation generalized eigenvalue problem
balancing procedure.  Called by @command{zgepbal}.
@end deftypefn


@anchor{doc-zgreduce}
@deftypefn {Function File} {} zgreduce (@var{sys}, @var{meps})
Implementation of procedure REDUCE in (Emami-Naeini and Van Dooren,
Automatica, # 1982).
@end deftypefn


@anchor{doc-zgrownorm}
@deftypefn {Function File} {[@var{nonz}, @var{zer}] =} zgrownorm (@var{mat}, @var{meps})
Return @var{nonz} = number of rows of @var{mat} whose two norm
exceeds @var{meps}, and @var{zer} = number of rows of mat whose two
norm is less than @var{meps}.
@end deftypefn


@anchor{doc-zgscal}
@deftypefn {Function File} {@var{x} =} zgscal (@var{f}, @var{z}, @var{n}, @var{m}, @var{p})
Generalized conjugate gradient iteration to
solve zero-computation generalized eigenvalue problem balancing equation
@math{fx=z}; called by @command{zgepbal}.
@end deftypefn


@anchor{doc-zgsgiv}
@deftypefn {Function File} {[a, b] =} zgsgiv (@var{c}, @var{s}, @var{a}, @var{b})
Apply givens rotation c,s to row vectors @var{a}, @var{b}.
No longer used in zero-balancing (__zgpbal__); kept for backward
compatibility.
@end deftypefn


@anchor{doc-zgshsr}
@deftypefn {Function File} {@var{x} =} zgshsr (@var{y})
Apply householder vector based on 
@iftex
@tex
$ e^m $
@end tex
@end iftex
@ifinfo
@math{e^(m)}
@end ifinfo
to column vector @var{y}.
Called by @command{zgfslv}.
@end deftypefn


@strong{References}
@table @strong
@item  ZGEP
 Hodel, @cite{Computation of Zeros with Balancing}, 1992, Linear Algebra
 and its Applications
@item @strong{Generalized CG}
 Golub and Van Loan, @cite{Matrix Computations, 2nd ed} 1989.
@end table

@node sysprop
@section System Analysis-Properties

@anchor{doc-analdemo}
@deftypefn {Function File} {} analdemo ()
Octave Controls toolbox demo: State Space analysis demo
@end deftypefn


@anchor{doc-abcddim}
@deftypefn {Function File} {[@var{n}, @var{m}, @var{p}] =} abcddim (@var{a}, @var{b}, @var{c}, @var{d})
Check for compatibility of the dimensions of the matrices defining
the linear system
@iftex
@tex
$[A, B, C, D]$ corresponding to
$$
\eqalign{
 {dx\over dt} &= A x + B u\cr
            y &= C x + D u}
$$
@end tex
@end iftex
@ifinfo
[A, B, C, D] corresponding to

@example
dx/dt = a x + b u
y = c x + d u
@end example

@end ifinfo
or a similar discrete-time system.

If the matrices are compatibly dimensioned, then @code{abcddim} returns

@table @var
@item n
The number of system states.

@item m
The number of system inputs.

@item p
The number of system outputs.
@end table

Otherwise @code{abcddim} returns @var{n} = @var{m} = @var{p} = @minus{}1.

Note: n = 0 (pure gain block) is returned without warning.
@seealso{is_abcd}
@end deftypefn


@anchor{doc-ctrb}
@deftypefn {Function File} {} ctrb (@var{sys}, @var{b})
@deftypefnx {Function File} {} ctrb (@var{a}, @var{b})
Build controllability matrix:
@iftex
@tex
$$ Q_s = [ B AB A^2B \ldots A^{n-1}B ] $$
@end tex
@end iftex
@ifinfo
@example
             2       n-1
Qs = [ B AB A B ... A   B ]
@end example
@end ifinfo

of a system data structure or the pair (@var{a}, @var{b}).

@command{ctrb} forms the controllability matrix.
The numerical properties of @command{is_controllable}
are much better for controllability tests.
@end deftypefn


@anchor{doc-h2norm}
@deftypefn {Function File} {} h2norm (@var{sys})
Computes the 
@iftex
@tex
$ { \cal H }_2 $
@end tex
@end iftex
@ifinfo
H-2
@end ifinfo
norm of a system data structure (continuous time only).

Reference:
Doyle, Glover, Khargonekar, Francis, @cite{State-Space Solutions to Standard} 
@iftex
@tex
$ { \cal H }_2 $ @cite{and} $ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
@cite{H-2 and H-infinity}
@end ifinfo
@cite{Control Problems}, @acronym{IEEE} @acronym{TAC} August 1989.
@end deftypefn


@anchor{doc-hinfnorm}
@deftypefn {Function File} {[@var{g}, @var{gmin}, @var{gmax}] =} hinfnorm (@var{sys}, @var{tol}, @var{gmin}, @var{gmax}, @var{ptol})
Computes the 
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
norm of a system data structure.

@strong{Inputs}
@table @var
@item sys
system data structure
@item tol
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
norm search tolerance (default: 0.001)
@item gmin
minimum value for norm search (default: 1e-9)
@item gmax
maximum value for norm search (default: 1e+9)
@item ptol
pole tolerance:
@itemize @bullet
@item if sys is continuous, poles with
@iftex
@tex
$ \vert {\rm real}(pole) \vert < ptol \Vert H \Vert $
@end tex
@end iftex
@ifinfo
@math{ |real(pole))| < ptol*||H|| }
@end ifinfo
(@var{H} is appropriate Hamiltonian)
are considered to be on the imaginary axis.

@item if sys is discrete, poles with
@iftex
@tex
$ \vert { \rm pole } - 1 \vert < ptol \Vert [ s_1 s_2 ] \Vert $
@end tex
@end iftex
@ifinfo
@math{|abs(pole)-1| < ptol*||[s1,s2]||}
@end ifinfo
(appropriate symplectic pencil)
are considered to be on the unit circle.

@item Default value: 1e-9
@end itemize
@end table

@strong{Outputs}
@table @var
@item g
Computed gain, within @var{tol} of actual gain.  @var{g} is returned as Inf
if the system is unstable.
@item gmin
@itemx gmax
Actual system gain lies in the interval [@var{gmin}, @var{gmax}].
@end table

References:
Doyle, Glover, Khargonekar, Francis, @cite{State-space solutions to standard}
@iftex
@tex
$ { \cal H }_2 $ @cite{and} $ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
@cite{H-2 and H-infinity}
@end ifinfo
@cite{control problems}, @acronym{IEEE} @acronym{TAC} August 1989;
Iglesias and Glover, @cite{State-Space approach to discrete-time}
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
@cite{H-infinity}
@end ifinfo
@cite{control}, Int. J. Control, vol 54, no. 5, 1991;
Zhou, Doyle, Glover, @cite{Robust and Optimal Control}, Prentice-Hall, 1996.
@end deftypefn


@anchor{doc-obsv}
@deftypefn {Function File} {} obsv (@var{sys}, @var{c})
@deftypefnx {Function File} {} obsv (@var{a}, @var{c})
Build observability matrix:
@iftex
@tex
$$ Q_b = \left[ \matrix{  C       \cr
                          CA    \cr
                          CA^2  \cr
                          \vdots  \cr
                          CA^{n-1} } \right ] $$
@end tex
@end iftex
@ifinfo
@example
@group
     | C        |
     | CA       |
Qb = | CA^2     |
     | ...      |
     | CA^(n-1) |
@end group
@end example
@end ifinfo
of a system data structure or the pair (@var{a}, @var{c}).

The numerical properties of @command{is_observable}
are much better for observability tests.
@end deftypefn


@anchor{doc-pzmap}
@deftypefn {Function File} {[@var{zer}, @var{pol}] =} pzmap (@var{sys})
Plots the zeros and poles of a system in the complex plane.

@strong{Input}
@table @var
@item sys
System data structure.
@end table

@strong{Outputs}
@table @var
@item pol
@item zer
if omitted, the poles and zeros are plotted on the screen.
otherwise, @var{pol} and @var{zer} are returned as the 
system poles and zeros (see @command{sys2zp} for a preferable function call).
@end table
@end deftypefn


@anchor{doc-is_abcd}
@deftypefn {Function File} {@var{retval} =} is_abcd (@var{a}, @var{b}, @var{c}, @var{d})
 Returns @var{retval} = 1 if the dimensions of @var{a}, @var{b},
@var{c}, @var{d} are compatible, otherwise @var{retval} = 0 with an
 appropriate diagnostic message printed to the screen.  The matrices
@var{b}, @var{c}, or @var{d} may be omitted.
@seealso{abcddim}
@end deftypefn


@anchor{doc-is_controllable}
@deftypefn {Function File} {[@var{retval}, @var{u}] =} is_controllable (@var{sys}, @var{tol})
@deftypefnx {Function File} {[@var{retval}, @var{u}] =} is_controllable (@var{a}, @var{b}, @var{tol})
Logical check for system controllability.

@strong{Inputs}
@table @var
@item sys
system data structure
@item a
@itemx b
@var{n} by @var{n}, @var{n} by @var{m} matrices, respectively
@item tol
optional roundoff parameter.  Default value: @code{10*eps}
@end table

@strong{Outputs}
@table @var
@item retval
Logical flag; returns true (1) if the system @var{sys} or the
pair (@var{a}, @var{b}) is controllable, whichever was passed as input
arguments.
@item u
@var{u} is an orthogonal basis of the controllable subspace.
@end table

@strong{Method}
Controllability is determined by applying Arnoldi iteration with
complete re-orthogonalization to obtain an orthogonal basis of the
Krylov subspace
@example
span ([b,a*b,...,a^@{n-1@}*b]).
@end example
The Arnoldi iteration is executed with @code{krylov} if the system
has a single input; otherwise a block Arnoldi iteration is performed
with @code{krylovb}.
@seealso{size, rows, columns, length, ismatrix, isscalar, isvector
is_observable, is_stabilizable, is_detectable, krylov, krylovb}
@end deftypefn


@anchor{doc-is_detectable}
@deftypefn {Function File} {@var{retval} =} is_detectable (@var{a}, @var{c}, @var{tol}, @var{dflg})
@deftypefnx {Function File} {@var{retval} =} is_detectable (@var{sys}, @var{tol})
Test for detectability (observability of unstable modes) of (@var{a}, @var{c}).

Returns 1 if the system @var{a} or the pair (@var{a}, @var{c}) is
detectable, 0 if not, and -1 if the system has unobservable modes at the
imaginary axis (unit circle for discrete-time systems).

@strong{See} @command{is_stabilizable} for detailed description of
arguments and computational method.
@seealso{is_stabilizable, size, rows, columns, length, ismatrix,
isscalar, isvector}
@end deftypefn


@anchor{doc-is_dgkf}
@deftypefn {Function File} {[@var{retval}, @var{dgkf_struct} ] =} is_dgkf (@var{asys}, @var{nu}, @var{ny}, @var{tol} )
Determine whether a continuous time state space system meets
assumptions of @acronym{DGKF} algorithm.
Partitions system into:
@example
[dx/dt]   [A  | Bw  Bu  ][w]
[ z   ] = [Cz | Dzw Dzu ][u]
[ y   ]   [Cy | Dyw Dyu ]
@end example
or similar discrete-time system.
If necessary, orthogonal transformations @var{qw}, @var{qz} and nonsingular
transformations @var{ru}, @var{ry} are applied to respective vectors
@var{w}, @var{z}, @var{u}, @var{y} in order to satisfy @acronym{DGKF} assumptions.
Loop shifting is used if @var{dyu} block is nonzero.

@strong{Inputs}
@table @var
@item         asys
system data structure
@item           nu
number of controlled inputs
@item        ny
number of measured outputs
@item        tol
threshold for 0; default: 200*@code{eps}.
@end table
@strong{Outputs}
@table @var
@item    retval
true(1) if system passes check, false(0) otherwise
@item    dgkf_struct
data structure of @command{is_dgkf} results.  Entries:
@table @var
@item      nw
@itemx     nz
dimensions of @var{w}, @var{z}
@item      a
system @math{A} matrix
@item      bw
(@var{n} x @var{nw}) @var{qw}-transformed disturbance input matrix
@item      bu
(@var{n} x @var{nu}) @var{ru}-transformed controlled input matrix;

@math{B = [Bw Bu]}
@item      cz
(@var{nz} x @var{n}) Qz-transformed error output matrix
@item      cy
(@var{ny} x @var{n}) @var{ry}-transformed measured output matrix

@math{C = [Cz; Cy]}
@item      dzu
@item      dyw
off-diagonal blocks of transformed system @math{D} matrix that enter
@var{z}, @var{y} from @var{u}, @var{w} respectively
@item      ru
controlled input transformation matrix
@item      ry
observed output transformation matrix
@item      dyu_nz
nonzero if the @var{dyu} block is nonzero.
@item      dyu
untransformed @var{dyu} block
@item      dflg
nonzero if the system is discrete-time
@end table
@end table
@code{is_dgkf} exits with an error if the system is mixed
discrete/continuous.

@strong{References}
@table @strong
@item [1]
Doyle, Glover, Khargonekar, Francis, @cite{State Space Solutions to Standard}
@iftex
@tex
$ { \cal H }_2 $ @cite{and} $ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
@cite{H-2 and H-infinity}
@end ifinfo
@cite{Control Problems}, @acronym{IEEE} @acronym{TAC} August 1989.
@item [2]
Maciejowksi, J.M., @cite{Multivariable Feedback Design}, Addison-Wesley, 1989.
@end table
@end deftypefn


@anchor{doc-is_digital}
@deftypefn {Function File} {@var{digital} =} is_digital (@var{sys}, @var{eflg})
Return nonzero if system is digital.

@strong{Inputs}
@table @var
@item sys
System data structure.
@item eflg
When equal to 0 (default value), exits with an error if the system 
is mixed (continuous and discrete components); when equal to 1, print
a warning if the system is mixed (continuous and discrete); when equal
to 2, operate silently.
@end table

@strong{Output}
@table @var
@item digital
When equal to 0, the system is purely continuous; when equal to 1, the
system is purely discrete; when equal to -1, the system is mixed continuous 
and discrete.
@end table
Exits with an error if @var{sys} is a mixed (continuous and discrete) system.
@end deftypefn


@anchor{doc-is_observable}
@deftypefn {Function File} {[@var{retval}, @var{u}] =} is_observable (@var{a}, @var{c}, @var{tol})
@deftypefnx {Function File} {[@var{retval}, @var{u}] =} is_observable (@var{sys}, @var{tol})
Logical check for system observability.

Default: tol = @code{tol = 10*norm(a,'fro')*eps}

Returns 1 if the system @var{sys} or the pair (@var{a}, @var{c}) is
observable, 0 if not.

See @command{is_controllable} for detailed description of arguments
and default values.
@seealso{size, rows, columns, length, ismatrix, isscalar, isvector}
@end deftypefn


@anchor{doc-is_sample}
@deftypefn {Function File} {} is_sample (@var{ts})
Return true if @var{ts} is a valid sampling time
(real, scalar, > 0).
@end deftypefn


@anchor{doc-is_siso}
@deftypefn {Function File} {} is_siso (@var{sys})
Returns nonzero if the system data structure
@var{sys} is single-input, single-output.
@end deftypefn


@anchor{doc-is_stabilizable}
@deftypefn {Function File} {@var{retval} =} is_stabilizable (@var{sys}, @var{tol})
@deftypefnx {Function File} {@var{retval} =} is_stabilizable (@var{a}, @var{b}, @var{tol}, @var{dflg})
Logical check for system stabilizability (i.e., all unstable modes are controllable). 
Returns 1 if the system is stabilizable, 0 if the system is not stabilizable, -1 
if the system has non stabilizable modes at the imaginary axis (unit circle for 
discrete-time systems.

Test for stabilizability is performed via Hautus Lemma. If 
@iftex
@tex
@var{dflg}$\neq$0
@end tex
@end iftex
@ifinfo 
@var{dflg}!=0
@end ifinfo
assume that discrete-time matrices (a,b) are supplied.
@seealso{size, rows, columns, length, ismatrix, isscalar, isvector
is_observable, is_stabilizable, is_detectable}
@end deftypefn


@anchor{doc-is_signal_list}
@deftypefn {Function File} {} is_signal_list (@var{mylist})
Return true if @var{mylist} is a list of individual strings.
@end deftypefn


@anchor{doc-is_stable}
@deftypefn {Function File} {} is_stable (@var{a}, @var{tol}, @var{dflg})
@deftypefnx {Function File} {} is_stable (@var{sys}, @var{tol})
Returns 1 if the matrix @var{a} or the system @var{sys}
is stable, or 0 if not.

@strong{Inputs}
@table @var
@item  tol
is a roundoff parameter, set to 200*@code{eps} if omitted.
@item dflg
Digital system flag (not required for system data structure):
@table @code
@item @var{dflg} != 0
stable if eig(a) is in the unit circle

@item @var{dflg} == 0
stable if eig(a) is in the open LHP (default)
@end table
@end table
@seealso{size, rows, columns, length, ismatrix, isscalar, isvector
is_observable, is_stabilizable, is_detectable, krylov, krylovb}
@end deftypefn


@node systime
@section System Analysis-Time Domain

@anchor{doc-c2d}
@deftypefn {Function File} {} c2d (@var{sys}, @var{opt}, @var{t})
@deftypefnx {Function File} {} c2d (@var{sys}, @var{t})

Converts the system data structure describing:
@iftex
@tex
$$ \dot x = A_cx + B_cu $$
@end tex
@end iftex
@ifinfo
@example
.
x = Ac x + Bc u
@end example
@end ifinfo
into a discrete time equivalent model:
@iftex
@tex
$$ x_{n+1} = A_dx_n + B_du_n $$
@end tex
@end iftex
@ifinfo
@example
x[n+1] = Ad x[n] + Bd u[n]
@end example
@end ifinfo
via the matrix exponential or bilinear transform.

@strong{Inputs}
@table @var
@item sys
system data structure (may have both continuous time and discrete
time subsystems)
@item opt
string argument; conversion option (optional argument;
may be omitted as shown above)
@table @code
@item "ex"
use the matrix exponential (default)
@item "bi"
use the bilinear transformation
@iftex
@tex
$$ s = { 2(z-1) \over T(z+1) } $$
@end tex
@end iftex
@ifinfo
@example
    2(z-1)
s = -----
    T(z+1)
@end example
@end ifinfo
FIXME: This option exits with an error if @var{sys} is not purely
continuous. (The @code{ex} option can handle mixed systems.)
@item "matched"
Use the matched pole/zero equivalent transformation (currently only
works for purely continuous @acronym{SISO} systems).
@end table
@item t
sampling time; required if @var{sys} is purely continuous.

@strong{Note} that if the second argument is not a string, @code{c2d()}
assumes that the second argument is @var{t} and performs 
appropriate argument checks.
@end table

@strong{Output}
@table @var
@item dsys 
Discrete time equivalent via zero-order hold, sample each @var{t} sec.
@end table

This function adds the suffix  @code{_d}
to the names of the new discrete states.
@end deftypefn


@anchor{doc-d2c}
@deftypefn {Function File} {} d2c (@var{sys}, @var{tol})
@deftypefnx {Function File} {} d2c (@var{sys}, @var{opt})
Convert a discrete (sub)system into a purely continuous one. 
The sampling time used is @code{sysgettsam(@var{sys})}.

@strong{Inputs}
@table @var
@item   sys
system data structure with discrete components
@item   tol
Scalar value.
Tolerance for convergence of default @code{"log"} option (see below)
@item   opt
conversion option.  Choose from:
@table @code
@item         "log"
(default) Conversion is performed via a matrix logarithm.
Due to some problems with this computation, it is
followed by a steepest descent algorithm to identify continuous time
@var{a}, @var{b}, to get a better fit to the original data.

If called as @code{d2c (@var{sys}, @var{tol})}, with @var{tol}
positive scalar, the @code{"log"} option is used.  The default value
for @var{tol} is @code{1e-8}.
@item        "bi"
Conversion is performed via bilinear transform
@math{z = (1 + s T / 2)/(1 - s T / 2)} where @math{T} is the
system sampling time (see @code{sysgettsam}).

FIXME: bilinear option exits with an error if @var{sys} is not purely
discrete
@end table
@end table
@strong{Output}
@table @var
@item csys 
continuous time system (same dimensions and signal names as in @var{sys}).
@end table
@end deftypefn


@anchor{doc-dmr2d}
@deftypefn {Function File} {[@var{dsys}, @var{fidx}] =} dmr2d (@var{sys}, @var{idx}, @var{sprefix}, @var{ts2}, @var{cuflg})
convert a multirate digital system to a single rate digital system
states specified by @var{idx}, @var{sprefix} are sampled at @var{ts2}, all
others are assumed sampled at @var{ts1} = @code{sysgettsam (@var{sys})}.

@strong{Inputs}
@table @var
@item   sys
discrete time system;
@code{dmr2d} exits with an error if @var{sys} is not discrete
@item   idx
indices or names of states with sampling time 
@code{sysgettsam(@var{sys})} (may be empty); see @code{cellidx}
@item   sprefix
list of string prefixes of states with sampling time
@code{sysgettsam(@var{sys})} (may be empty)
@item   ts2
sampling time of states not specified by @var{idx}, @var{sprefix}
must be an integer multiple of @code{sysgettsam(@var{sys})}
@item   cuflg
"constant u flag" if @var{cuflg} is nonzero then the system inputs are
assumed to be constant over the revised sampling interval @var{ts2}.
Otherwise, since the inputs can change during the interval
@var{t} in @math{[k ts2, (k+1) ts2]}, an additional set of inputs is
included in the revised B matrix so that these intersample inputs
may be included in the single-rate system.
default @var{cuflg} = 1.
@end table

@strong{Outputs}
@table @var
@item   dsys
equivalent discrete time system with sampling time @var{ts2}.

The sampling time of sys is updated to @var{ts2}.

if @var{cuflg}=0 then a set of additional inputs is added to
the system with suffixes _d1, @dots{}, _dn to indicate their
delay from the starting time k @var{ts2}, i.e.
u = [u_1; u_1_d1; @dots{}, u_1_dn] where u_1_dk is the input
k*ts1 units of time after u_1 is sampled. (@var{ts1} is
the original sampling time of the discrete time system and
@var{ts2} = (n+1)*ts1)

@item   fidx
indices of "formerly fast" states specified by @var{idx} and @var{sprefix};
these states are updated to the new (slower) sampling interval @var{ts2}.
@end table

@strong{WARNING} Not thoroughly tested yet; especially when
@var{cuflg} == 0.
@end deftypefn


@anchor{doc-damp}
@deftypefn {Function File} {} damp (@var{p}, @var{tsam})
Displays eigenvalues, natural frequencies and damping ratios
of the eigenvalues of a matrix @var{p} or the @math{A} matrix of a
system @var{p}, respectively.
If @var{p} is a system, @var{tsam} must not be specified.
If @var{p} is a matrix and @var{tsam} is specified, eigenvalues
of @var{p} are assumed to be in @var{z}-domain.
@seealso{eig}
@end deftypefn


@anchor{doc-dcgain}
@deftypefn {Function File} {} dcgain (@var{sys}, @var{tol})
Returns dc-gain matrix. If dc-gain is infinite
an empty matrix is returned.
The argument @var{tol} is an optional tolerance for the condition
number of the @math{A} Matrix in @var{sys} (default @var{tol} = 1.0e-10)
@end deftypefn


@anchor{doc-impulse}
@deftypefn {Function File} {[@var{y}, @var{t}] =} impulse (@var{sys}, @var{inp}, @var{tstop}, @var{n})
Impulse response for a linear system.
The system can be discrete or multivariable (or both).
If no output arguments are specified, @code{impulse}
produces a plot or the impulse response data for system @var{sys}.

@strong{Inputs}
@table @var
@item sys
System data structure.
@item inp
Index of input being excited
@item tstop
The argument @var{tstop} (scalar value) denotes the time when the
simulation should end.
@item n
the number of data values.

Both parameters @var{tstop} and @var{n} can be omitted and will be
computed from the eigenvalues of the A Matrix.
@end table
@strong{Outputs}
@table @var
@item y
Values of the impulse response.
@item t
Times of the impulse response.
@end table
@seealso{step}
@end deftypefn


@anchor{doc-step}
@deftypefn {Function File} {[@var{y}, @var{t}] =} step (@var{sys}, @var{inp}, @var{tstop}, @var{n})
Step response for a linear system.
The system can be discrete or multivariable (or both).
If no output arguments are specified, @code{step}
produces a plot or the step response data for system @var{sys}.

@strong{Inputs}
@table @var
@item sys
System data structure.
@item inp
Index of input being excited
@item tstop
The argument @var{tstop} (scalar value) denotes the time when the
simulation should end.
@item n
the number of data values.

Both parameters @var{tstop} and @var{n} can be omitted and will be
computed from the eigenvalues of the A Matrix.
@end table
@strong{Outputs}
@table @var
@item y
Values of the step response.
@item t
Times of the step response.
@end table

When invoked with the output parameter @var{y} the plot is not displayed.
@seealso{impulse}
@end deftypefn


@node sysfreq
@section System Analysis-Frequency Domain

@strong{Demonstration/tutorial script}
@anchor{doc-frdemo}
@deftypefn {Function File} {} frdemo ()
Octave Control Toolbox demo: Frequency Response demo.
@end deftypefn


@anchor{doc-bode}
@deftypefn {Function File} {[@var{mag}, @var{phase}, @var{w}] =} bode (@var{sys}, @var{w}, @var{out_idx}, @var{in_idx})
If no output arguments are given: produce Bode plots of a system; otherwise,
compute the frequency response of a system data structure

@strong{Inputs}
@table @var
@item   sys
a system data structure (must be either purely continuous or discrete;
see is_digital)
@item   w
frequency values for evaluation.

if @var{sys} is continuous, then bode evaluates @math{G(jw)} where
@math{G(s)} is the system transfer function.

if @var{sys} is discrete, then bode evaluates G(@code{exp}(jwT)), where
@itemize @bullet
@item @math{T} is the system sampling time
@item @math{G(z)} is the system transfer function.
@end itemize

@strong{Default} the default frequency range is selected as follows: (These
steps are @strong{not} performed if @var{w} is specified)
@enumerate
@item via routine __bodquist__, isolate all poles and zeros away from
@var{w}=0 (@var{jw}=0 or @math{@code{exp}(jwT)}=1) and select the frequency
range based on the breakpoint locations of the frequencies.
@item if @var{sys} is discrete time, the frequency range is limited
              to @math{jwT} in
@ifinfo
[0,2 pi /T]
@end ifinfo
@iftex
@tex
$[0,2\pi/T]$
@end tex
@end iftex
@item A "smoothing" routine is used to ensure that the plot phase does
not change excessively from point to point and that singular
points (e.g., crossovers from +/- 180) are accurately shown.

@end enumerate
@item out_idx
@itemx in_idx

The names or indices of outputs and inputs to be used in the frequency
response.  See @code{sysprune}.

@strong{Example}
@example
bode(sys,[],"y_3", @{"u_1","u_4"@});
@end example
@end table
@strong{Outputs}
@table @var
@item mag
@itemx phase
the magnitude and phase of the frequency response @math{G(jw)} or
@math{G(@code{exp}(jwT))} at the selected frequency values.
@item w
the vector of frequency values used
@end table

@enumerate
@item If no output arguments are given, e.g.,
@example
bode(sys);
@end example
bode plots the results to the screen.  Descriptive labels are
automatically placed.

Failure to include a concluding semicolon will yield some garbage
being printed to the screen (@code{ans = []}).

@item If the requested plot is for an @acronym{MIMO} system, mag is set to
@math{||G(jw)||} or @math{||G(@code{exp}(jwT))||}
and phase information is not computed.
@end enumerate
@end deftypefn


@anchor{doc-bode_bounds}
@deftypefn {Function File} {[@var{wmin}, @var{wmax}] =} bode_bounds (@var{zer}, @var{pol}, @var{dflg}, @var{tsam})
Get default range of frequencies based on cutoff frequencies of system
poles and zeros.
Frequency range is the interval
@iftex
@tex
$ [ 10^{w_{min}}, 10^{w_{max}} ] $
@end tex
@end iftex
@ifinfo
[10^@var{wmin}, 10^@var{wmax}]
@end ifinfo

Used internally in @command{__freqresp__} (@command{bode}, @command{nyquist})
@end deftypefn


@anchor{doc-freqchkw}
@deftypefn {Function File} {} freqchkw (@var{w})
Used by @command{__freqresp__} to check that input frequency vector @var{w}
is valid.
Returns boolean value.
@end deftypefn


@anchor{doc-ltifr}
@deftypefn {Function File} {@var{out} =} ltifr (@var{a}, @var{b}, @var{w})
@deftypefnx {Function File} {@var{out} =} ltifr (@var{sys}, @var{w})
Linear time invariant frequency response of single-input systems.

@strong{Inputs}
@table @var
@item a
@itemx b
coefficient matrices of @math{dx/dt = A x + B u}
@item sys
system data structure
@item w
vector of frequencies
@end table
@strong{Output}
@table @var
@item out
frequency response, that is:
@end table
@iftex
@tex
$$ G(j\omega) = (j\omega I-A)^{-1}B $$
@end tex
@end iftex
@ifinfo
@example
                           -1
             G(s) = (jw I-A) B
@end example
@end ifinfo
for complex frequencies @math{s = jw}.
@end deftypefn


@anchor{doc-nyquist}
@deftypefn {Function File} {[@var{realp}, @var{imagp}, @var{w}] =} nyquist (@var{sys}, @var{w}, @var{out_idx}, @var{in_idx}, @var{atol})
@deftypefnx {Function File} {} nyquist (@var{sys}, @var{w}, @var{out_idx}, @var{in_idx}, @var{atol})
Produce Nyquist plots of a system; if no output arguments are given, Nyquist
plot is printed to the screen.

Compute the frequency response of a system.

@strong{Inputs} (pass as empty to get default values)
@table @var
@item sys
system data structure (must be either purely continuous or discrete;
see @code{is_digital})
@item w
frequency values for evaluation.
If sys is continuous, then bode evaluates @math{G(@var{jw})}; 
if sys is discrete, then bode evaluates @math{G(exp(@var{jwT}))},
where @var{T} is the system sampling time.
@item default
the default frequency range is selected as follows: (These
steps are @strong{not} performed if @var{w} is specified)
@enumerate
@item via routine @command{__bodquist__}, isolate all poles and zeros away from
@var{w}=0 (@var{jw}=0 or @math{exp(@var{jwT})=1}) and select the frequency
range based on the breakpoint locations of the frequencies.
@item if @var{sys} is discrete time, the frequency range is limited
to @var{jwT} in
@ifinfo
[0,2p*pi]
@end ifinfo
@iftex
@tex
$ [ 0,2  p \pi ] $
@end tex
@end iftex
@item A ``smoothing'' routine is used to ensure that the plot phase does
not change excessively from point to point and that singular
points (e.g., crossovers from +/- 180) are accurately shown.
@end enumerate
@item   atol
for interactive nyquist plots: atol is a change-in-slope tolerance
for the of asymptotes (default = 0; 1e-2 is a good choice).  This allows
the user to ``zoom in'' on portions of the Nyquist plot too small to be
seen with large asymptotes.
@end table
@strong{Outputs}
@table @var
@item    realp
@itemx   imagp
the real and imaginary parts of the frequency response
@math{G(jw)} or @math{G(exp(jwT))} at the selected frequency values.
@item w
the vector of frequency values used
@end table

If no output arguments are given, nyquist plots the results to the screen.
If @var{atol} != 0 and asymptotes are detected then the user is asked
interactively if they wish to zoom in (remove asymptotes)
Descriptive labels are automatically placed.

Note: if the requested plot is for an @acronym{MIMO} system, a warning message is
presented; the returned information is of the magnitude
@iftex
@tex
$ \Vert G(jw) \Vert $ or $ \Vert G( {\rm exp}(jwT) \Vert $
@end tex
@end iftex
@ifinfo
||G(jw)|| or ||G(exp(jwT))||
@end ifinfo
only; phase information is not computed.
@end deftypefn


@anchor{doc-nichols}
@deftypefn {Function File} {[@var{mag}, @var{phase}, @var{w}] =} nichols (@var{sys}, @var{w}, @var{outputs}, @var{inputs})
Produce Nichols plot of a system.

@strong{Inputs}
@table @var
@item sys
System data structure (must be either purely continuous or discrete; 
see @command{is_digital}).
@item w
Frequency values for evaluation.
@itemize
@item if sys is continuous, then nichols evaluates @math{G(jw)}.
@item if sys is discrete, then nichols evaluates @math{G(exp(jwT))}, 
where @var{T}=@var{sys}. @var{tsam} is the system sampling time.
@item the default frequency range is selected as follows (These
       steps are @strong{not} performed if @var{w} is specified):
@enumerate
@item via routine @command{__bodquist__}, isolate all poles and zeros away from
@var{w}=0 (@math{jw=0} or @math{exp(jwT)=1}) and select the frequency range 
based on the breakpoint locations of the frequencies.
@item if sys is discrete time, the frequency range is limited to jwT in 
@iftex
@tex
$ [0, 2p\pi] $.
@end tex
@end iftex
@ifinfo
[0,2p*pi].
@end ifinfo
@item A ``smoothing'' routine is used to ensure that the plot phase does
not change excessively from point to point and that singular points 
(e.g., crossovers from +/- 180) are accurately shown.
@end enumerate
@end itemize
@item outputs
@itemx inputs
the names or indices of the output(s) and input(s) to be used in the 
frequency response; see @command{sysprune}.
@end table
@strong{Outputs}
@table @var
@item mag
@itemx phase
The magnitude and phase of the frequency response @math{G(jw)} or 
@math{G(exp(jwT))} at the selected frequency values.
@item w
The vector of frequency values used.
@end table
If no output arguments are given, @command{nichols} plots the results to the screen.
Descriptive labels are automatically placed. See @command{xlabel}, 
@command{ylabel}, and @command{title}.

Note: if the requested plot is for an @acronym{MIMO} system, @var{mag} is set to
@iftex
@tex
$ \Vert G(jw) \Vert $ or $ \Vert G( {\rm exp}(jwT) \Vert $
@end tex
@end iftex
@ifinfo
||G(jw)|| or ||G(exp(jwT))||
@end ifinfo
and phase information is not computed.
@end deftypefn


@anchor{doc-tzero}
@deftypefn {Function File} {[@var{zer}, @var{gain}] =} tzero (@var{a}, @var{b}, @var{c}, @var{d}, @var{opt})
@deftypefnx {Function File} {[@var{zer}, @var{gain}] =} tzero (@var{sys}, @var{opt})
Compute transmission zeros of a continuous system:
@iftex
@tex
$$ \dot x = Ax + Bu $$
$$ y = Cx + Du $$
@end tex
@end iftex
@ifinfo
@example
.
x = Ax + Bu
y = Cx + Du
@end example
@end ifinfo
or of a discrete one:
@iftex
@tex
$$ x_{k+1} = Ax_k + Bu_k $$
$$ y_k = Cx_k + Du_k $$
@end tex
@end iftex
@ifinfo
@example
x(k+1) = A x(k) + B u(k)
y(k)   = C x(k) + D u(k)
@end example
@end ifinfo

@strong{Outputs}
@table @var
@item zer
 transmission zeros of the system
@item gain
leading coefficient (pole-zero form) of @acronym{SISO} transfer function
returns gain=0 if system is multivariable
@end table
@strong{References}
@enumerate
@item Emami-Naeini and Van Dooren, Automatica, 1982.
@item Hodel, @cite{Computation of Zeros with Balancing}, 1992 Lin. Alg. Appl.
@end enumerate
@end deftypefn


@anchor{doc-tzero2}
@deftypefn {Function File} {@var{zr} =} tzero2 (@var{a}, @var{b}, @var{c}, @var{d}, @var{bal})
Compute the transmission zeros of @var{a}, @var{b}, @var{c}, @var{d}.

@var{bal} = balancing option (see balance); default is @code{"B"}.

Needs to incorporate @command{mvzero} algorithm to isolate finite zeros; 
use @command{tzero} instead.
@end deftypefn


@node cacsd
@section Controller Design

@anchor{doc-dgkfdemo}
@deftypefn {Function File} {} dgkfdemo ()
Octave Controls toolbox demo: 
@iftex
@tex
$ { \cal H }_2 $/$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-2/H-infinity
@end ifinfo
options demos.
@end deftypefn


@anchor{doc-hinfdemo}
@deftypefn {Function File} {} hinfdemo ()

@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
design demos for continuous @acronym{SISO} and @acronym{MIMO} systems and a
discrete system.  The @acronym{SISO} system is difficult to control because
it is non-minimum-phase and unstable. The second design example
controls the @command{jet707} plant, the linearized state space model of a
Boeing 707-321 aircraft at @var{v}=80 m/s 
@iftex
@tex
($M = 0.26$, $G_{a0} = -3^{\circ}$, ${\alpha}_0 = 4^{\circ}$, ${\kappa}= 50^{\circ}$).
@end tex
@end iftex
@ifinfo
(@var{M} = 0.26, @var{Ga0} = -3 deg, @var{alpha0} = 4 deg, @var{kappa} = 50 deg).
@end ifinfo
Inputs: (1) thrust and (2) elevator angle
Outputs: (1) airspeed and (2) pitch angle. The discrete system is a
stable and second order.

@table @asis
@item @acronym{SISO} plant:

@iftex
@tex
$$ G(s) = { s-2 \over (s+2) (s-1) } $$
@end tex
@end iftex
@ifinfo
@example
@group
                s - 2
     G(s) = --------------
            (s + 2)(s - 1)
@end group
@end example
@end ifinfo

@smallexample
@group

                              +----+
         -------------------->| W1 |---> v1
     z   |                    +----+
     ----|-------------+
         |             |
         |    +---+    v   y  +----+
       u *--->| G |--->O--*-->| W2 |---> v2
         |    +---+       |   +----+
         |                |
         |    +---+       |
         -----| K |<-------
              +---+
@end group
@end smallexample

@iftex
@tex
$$ { \rm min } \Vert T_{vz} \Vert _\infty $$
@end tex
@end iftex
@ifinfo
@example
min || T   ||
        vz   infty
@end example
@end ifinfo

@var{W1} und @var{W2} are the robustness and performance weighting
functions.

@item @acronym{MIMO} plant:
The optimal controller minimizes the 
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
norm of the
augmented plant @var{P} (mixed-sensitivity problem):
@smallexample
@group
     w
      1 -----------+
                   |                   +----+
               +---------------------->| W1 |----> z1
     w         |   |                   +----+
      2 ------------------------+
               |   |            |
               |   v   +----+   v      +----+
            +--*-->o-->| G  |-->o--*-->| W2 |---> z2
            |          +----+      |   +----+
            |                      |
            ^                      v
            u                       y (to K)
         (from controller K)
@end group
@end smallexample

@iftex
@tex
$$ \left [ \matrix{ z_1 \cr
                    z_2 \cr
                    y   } \right ] =  
 P \left [ \matrix{ w_1 \cr
                    w_2 \cr
                    u   } \right ] $$
@end tex
@end iftex
@ifinfo
@smallexample
@group
                  +    +           +    +
                  | z  |           | w  |
                  |  1 |           |  1 |
                  | z  | = [ P ] * | w  |
                  |  2 |           |  2 |
                  | y  |           | u  |
                  +    +           +    +
@end group
@end smallexample
@end ifinfo

@item Discrete system:
This is not a true discrete design. The design is carried out
in continuous time while the effect of sampling is described by
a bilinear transformation of the sampled system.
This method works quite well if the sampling period is ``small''
compared to the plant time constants.

@item The continuous plant:
@iftex
@tex
$$ G(s) = { 1 \over (s+2)(s+1) } $$
@end tex
@end iftex

@ifinfo
@example
@group
                   1
     G (s) = --------------
      k      (s + 2)(s + 1)

@end group
@end example
@end ifinfo

is discretised with a @acronym{ZOH} (Sampling period = @var{Ts} = 1 second):
@iftex
@tex
$$ G(z) = { 0.199788z + 0.073498 \over (z - 0.36788) (z - 0.13534) } $$
@end tex
@end iftex
@ifinfo
@example
@group

               0.199788z + 0.073498
     G(z) = --------------------------
            (z - 0.36788)(z - 0.13534)
@end group
@end example
@end ifinfo

@smallexample
@group

                              +----+
         -------------------->| W1 |---> v1
     z   |                    +----+
     ----|-------------+
         |             |
         |    +---+    v      +----+
         *--->| G |--->O--*-->| W2 |---> v2
         |    +---+       |   +----+
         |                |
         |    +---+       |
         -----| K |<-------
              +---+
@end group
@end smallexample
@iftex
@tex
$$ { \rm min } \Vert T_{vz} \Vert _\infty $$
@end tex
@end iftex
@ifinfo
@example
min || T   ||
        vz   infty
@end example
@end ifinfo
@var{W1} and @var{W2} are the robustness and performance weighting
functions.
@end table
@end deftypefn


@anchor{doc-dlqe}
@deftypefn {Function File} {[@var{l}, @var{m}, @var{p}, @var{e}] =} dlqe (@var{a}, @var{g}, @var{c}, @var{sigw}, @var{sigv}, @var{z})
Construct the linear quadratic estimator (Kalman filter) for the
discrete time system
@iftex
@tex
$$
 x_{k+1} = A x_k + B u_k + G w_k
$$
$$
 y_k = C x_k + D u_k + v_k
$$
@end tex
@end iftex
@ifinfo

@example
x[k+1] = A x[k] + B u[k] + G w[k]
  y[k] = C x[k] + D u[k] + v[k]
@end example

@end ifinfo
where @var{w}, @var{v} are zero-mean gaussian noise processes with
respective intensities @code{@var{sigw} = cov (@var{w}, @var{w})} and
@code{@var{sigv} = cov (@var{v}, @var{v})}.

If specified, @var{z} is @code{cov (@var{w}, @var{v})}.  Otherwise
@code{cov (@var{w}, @var{v}) = 0}.

The observer structure is
@iftex
@tex
$$
 z_{k|k} = z_{k|k-1} + l (y_k - C z_{k|k-1} - D u_k)
$$
$$
 z_{k+1|k} = A z_{k|k} + B u_k
$$
@end tex
@end iftex
@ifinfo

@example
z[k|k] = z[k|k-1] + L (y[k] - C z[k|k-1] - D u[k])
z[k+1|k] = A z[k|k] + B u[k]
@end example
@end ifinfo

@noindent
The following values are returned:

@table @var
@item l
The observer gain,
@iftex
@tex
$(A - ALC)$.
@end tex
@end iftex
@ifinfo
(@var{a} - @var{a}@var{l}@var{c}).
@end ifinfo
is stable.

@item m
The Riccati equation solution.

@item p
The estimate error covariance after the measurement update.

@item e
The closed loop poles of
@iftex
@tex
$(A - ALC)$.
@end tex
@end iftex
@ifinfo
(@var{a} - @var{a}@var{l}@var{c}).
@end ifinfo
@end table
@end deftypefn


@anchor{doc-dlqr}
@deftypefn {Function File} {[@var{k}, @var{p}, @var{e}] =} dlqr (@var{a}, @var{b}, @var{q}, @var{r}, @var{z})
Construct the linear quadratic regulator for the discrete time system
@iftex
@tex
$$
 x_{k+1} = A x_k + B u_k
$$
@end tex
@end iftex
@ifinfo

@example
x[k+1] = A x[k] + B u[k]
@end example

@end ifinfo
to minimize the cost functional
@iftex
@tex
$$
 J = \sum x^T Q x + u^T R u
$$
@end tex
@end iftex
@ifinfo

@example
J = Sum (x' Q x + u' R u)
@end example
@end ifinfo

@noindent
@var{z} omitted or
@iftex
@tex
$$
 J = \sum x^T Q x + u^T R u + 2 x^T Z u
$$
@end tex
@end iftex
@ifinfo

@example
J = Sum (x' Q x + u' R u + 2 x' Z u)
@end example

@end ifinfo
@var{z} included.

The following values are returned:

@table @var
@item k
The state feedback gain,
@iftex
@tex
$(A - B K)$
@end tex
@end iftex
@ifinfo
(@var{a} - @var{b}@var{k})
@end ifinfo
is stable.

@item p
The solution of algebraic Riccati equation.

@item e
The closed loop poles of
@iftex
@tex
$(A - B K)$.
@end tex
@end iftex
@ifinfo
(@var{a} - @var{b}@var{k}).
@end ifinfo
@end table
@end deftypefn


@anchor{doc-dkalman}
@deftypefn {Function File} {[@var{Lp}, @var{Lf}, @var{P}, @var{Z}] =} dkalman (@var{A}, @var{G}, @var{C}, @var{Qw}, @var{Rv}, @var{S})
Construct the linear quadratic estimator (Kalman predictor) for the
discrete time system
@iftex
@tex
$$
 x_{k+1} = A x_k + B u_k + G w_k
$$
$$
 y_k = C x_k + D u_k + v_k
$$
@end tex
@end iftex
@ifinfo

@example
x[k+1] = A x[k] + B u[k] + G w[k]
  y[k] = C x[k] + D u[k] + v[k]
@end example

@end ifinfo
where @var{w}, @var{v} are zero-mean gaussian noise processes with
respective intensities @code{@var{Qw} = cov (@var{w}, @var{w})} and
@code{@var{Rv} = cov (@var{v}, @var{v})}.

If specified, @var{S} is @code{cov (@var{w}, @var{v})}.  Otherwise
@code{cov (@var{w}, @var{v}) = 0}.

The observer structure is
@iftex
@tex
$x_{k+1|k} = A x_{k|k-1} + B u_k + L_p (y_k - C x_{k|k-1} - D u_k)$
$x_{k|k} = x_{k|k} + L_f (y_k - C x_{k|k-1} - D u_k)$
@end tex
@end iftex
@ifinfo

@example
x[k+1|k] = A x[k|k-1] + B u[k] + LP (y[k] - C x[k|k-1] - D u[k])
x[k|k] = x[k|k-1] + LF (y[k] - C x[k|k-1] - D u[k])
@end example
@end ifinfo

@noindent
The following values are returned:

@table @var
@item Lp
The predictor gain,
@iftex
@tex
$(A - L_p C)$.
@end tex
@end iftex
@ifinfo
(@var{A} - @var{Lp} @var{C})
@end ifinfo
is stable.

@item Lf
The filter gain.

@item P
The Riccati solution. 
@iftex
@tex
$P = E \{(x - x_{n|n-1})(x - x_{n|n-1})'\}$
@end tex
@end iftex

@ifinfo
P = E [(x - x[n|n-1])(x - x[n|n-1])']
@end ifinfo

@item Z
The updated error covariance matrix.
@iftex
@tex
$Z = E \{(x - x_{n|n})(x - x_{n|n})'\}$
@end tex
@end iftex

@ifinfo
Z = E [(x - x[n|n])(x - x[n|n])']
@end ifinfo
@end table
@end deftypefn


@anchor{doc-h2syn}
@deftypefn {Function File} {[@var{K}, @var{gain}, @var{kc}, @var{kf}, @var{pc}, @var{pf}] = } h2syn (@var{asys}, @var{nu}, @var{ny}, @var{tol})
Design 
@iftex
@tex
$ { \cal H }_2 $
@end tex
@end iftex
@ifinfo
H-2
@end ifinfo
optimal controller per procedure in 
Doyle, Glover, Khargonekar, Francis, @cite{State-Space Solutions to Standard}
@iftex
@tex
$ { \cal H }_2 $ @cite{and} $ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
@cite{H-2 and H-infinity}
@end ifinfo
@cite{Control Problems}, @acronym{IEEE} @acronym{TAC} August 1989.

Discrete-time control per Zhou, Doyle, and Glover, @cite{Robust and optimal control}, Prentice-Hall, 1996.

@strong{Inputs}
@table @var
@item asys
system data structure (see ss, sys2ss)
@itemize @bullet
@item controller is implemented for continuous time systems
@item controller is @strong{not} implemented for discrete time systems
@end itemize
@item nu
number of controlled inputs
@item ny
number of measured outputs
@item tol
threshold for 0.  Default: 200*@code{eps}
@end table

@strong{Outputs}
@table @var
@item    k
system controller
@item    gain
optimal closed loop gain
@item    kc
full information control (packed)
@item    kf
state estimator (packed)
@item    pc
@acronym{ARE} solution matrix for regulator subproblem
@item    pf
@acronym{ARE} solution matrix for filter subproblem
@end table
@end deftypefn


@anchor{doc-hinf_ctr}
@deftypefn {Function File} {@var{K} =} hinf_ctr (@var{dgs}, @var{f}, @var{h}, @var{z}, @var{g})
Called by @code{hinfsyn} to compute the 
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
optimal controller.

@strong{Inputs}
@table @var
@item dgs
data structure returned by @code{is_dgkf}
@item f
@itemx h
feedback and filter gain (not partitioned)
@item g
final gamma value
@end table
@strong{Outputs}
@table @var
@item K
controller (system data structure)
@end table

Do not attempt to use this at home; no argument checking performed.
@end deftypefn


@anchor{doc-hinfsyn}
@deftypefn {Function File} {[@var{k}, @var{g}, @var{gw}, @var{xinf}, @var{yinf}] =} hinfsyn (@var{asys}, @var{nu}, @var{ny}, @var{gmin}, @var{gmax}, @var{gtol}, @var{ptol}, @var{tol})

@strong{Inputs} input system is passed as either
@table @var
@item asys
system data structure (see @command{ss}, @command{sys2ss})
@itemize @bullet
@item controller is implemented for continuous time systems
@item controller is @strong{not} implemented for discrete time systems  (see
bilinear transforms in @command{c2d}, @command{d2c})
@end itemize
@item nu
number of controlled inputs
@item ny
number of measured outputs
@item gmin
initial lower bound on 
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
optimal gain
@item gmax
initial upper bound on 
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
Optimal gain.
@item gtol
Gain threshold.  Routine quits when @var{gmax}/@var{gmin} < 1+tol.
@item ptol
poles with @code{abs(real(pole))} 
@iftex
@tex
$ < ptol \Vert H \Vert $
@end tex
@end iftex
@ifinfo
< ptol*||H|| 
@end ifinfo
(@var{H} is appropriate
Hamiltonian) are considered to be on the imaginary axis.
Default: 1e-9.
@item tol
threshold for 0.  Default: 200*@code{eps}.

@var{gmax}, @var{min}, @var{tol}, and @var{tol} must all be positive scalars.
@end table
@strong{Outputs}
@table @var
@item k
System controller.
@item g
Designed gain value.
@item gw
Closed loop system.
@item xinf
@acronym{ARE} solution matrix for regulator subproblem.
@item yinf
@acronym{ARE} solution matrix for filter subproblem.
@end table

References:
@enumerate
@item Doyle, Glover, Khargonekar, Francis, @cite{State-Space Solutions
to Standard}
@iftex
@tex
$ { \cal H }_2 $ @cite{and} $ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
@cite{H-2 and H-infinity}
@end ifinfo
@cite{Control Problems}, @acronym{IEEE} @acronym{TAC} August 1989.

@item Maciejowksi, J.M., @cite{Multivariable feedback design},
Addison-Wesley, 1989, @acronym{ISBN} 0-201-18243-2.

@item Keith Glover and John C. Doyle, @cite{State-space formulae for all
stabilizing controllers that satisfy an}
@iftex
@tex
$ { \cal H }_\infty $@cite{norm}
@end tex
@end iftex
@ifinfo
@cite{H-infinity-norm}
@end ifinfo
@cite{bound and relations to risk sensitivity},
Systems & Control Letters 11, Oct. 1988, pp 167--172.
@end enumerate
@end deftypefn


@anchor{doc-hinfsyn_chk}
@deftypefn {Function File} {[@var{retval}, @var{pc}, @var{pf}] =} hinfsyn_chk (@var{a}, @var{b1}, @var{b2}, @var{c1}, @var{c2}, @var{d12}, @var{d21}, @var{g}, @var{ptol})
Called by @code{hinfsyn} to see if gain @var{g} satisfies conditions in
Theorem 3 of
Doyle, Glover, Khargonekar, Francis, @cite{State Space Solutions to Standard}
@iftex
@tex
$ { \cal H }_2 $ @cite{and} $ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
@cite{H-2 and H-infinity}
@end ifinfo
@cite{Control Problems}, @acronym{IEEE} @acronym{TAC} August 1989.

@strong{Warning:} do not attempt to use this at home; no argument
checking performed.

@strong{Inputs}

As returned by @code{is_dgkf}, except for:
@table @var
@item g
candidate gain level
@item ptol
 as in @code{hinfsyn}
@end table

@strong{Outputs}
@table @var
@item retval
 1 if g exceeds optimal Hinf closed loop gain, else 0
@item pc
solution of ``regulator'' 
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
@acronym{ARE}
@item pf
solution of ``filter''
@iftex
@tex
$ { \cal H }_\infty $
@end tex
@end iftex
@ifinfo
H-infinity
@end ifinfo
@acronym{ARE}
@end table
Do not attempt to use this at home; no argument checking performed.
@end deftypefn


@anchor{doc-hinfsyn_ric}
@deftypefn {Function File} {[@var{xinf}, @var{x_ha_err}] =} hinfsyn_ric (@var{a}, @var{bb}, @var{c1}, @var{d1dot}, @var{r}, @var{ptol})
Forms
@example
xx = ([bb; -c1'*d1dot]/r) * [d1dot'*c1 bb'];
Ha = [a 0*a; -c1'*c1 - a'] - xx;
@end example
and solves associated Riccati equation.
The error code @var{x_ha_err} indicates one of the following
conditions:
@table @asis
@item 0
successful
@item 1
@var{xinf} has imaginary eigenvalues
@item 2
@var{hx} not Hamiltonian
@item 3
@var{xinf} has infinite eigenvalues (numerical overflow)
@item 4
@var{xinf} not symmetric
@item 5
@var{xinf} not positive definite
@item 6
@var{r} is singular
@end table
@end deftypefn


@anchor{doc-lqe}
@deftypefn {Function File} {[@var{k}, @var{p}, @var{e}] =} lqe (@var{a}, @var{g}, @var{c}, @var{sigw}, @var{sigv}, @var{z})
Construct the linear quadratic estimator (Kalman filter) for the
continuous time system
@iftex
@tex
$$
 {dx\over dt} = A x + G u
$$
$$
 y = C x + v
$$
@end tex
@end iftex
@ifinfo

@example
dx
-- = A x + G u
dt

y = C x + v
@end example

@end ifinfo
where @var{w} and @var{v} are zero-mean gaussian noise processes with
respective intensities

@example
sigw = cov (w, w)
sigv = cov (v, v)
@end example

The optional argument @var{z} is the cross-covariance
@code{cov (@var{w}, @var{v})}.  If it is omitted,
@code{cov (@var{w}, @var{v}) = 0} is assumed.

Observer structure is @code{dz/dt = A z + B u + k (y - C z - D u)}

The following values are returned:

@table @var
@item k
The observer gain,
@iftex
@tex
$(A - K C)$
@end tex
@end iftex
@ifinfo
(@var{a} - @var{k}@var{c})
@end ifinfo
is stable.

@item p
The solution of algebraic Riccati equation.

@item e
The vector of closed loop poles of
@iftex
@tex
$(A - K C)$.
@end tex
@end iftex
@ifinfo
(@var{a} - @var{k}@var{c}).
@end ifinfo
@end table
@end deftypefn


@anchor{doc-lqg}
@deftypefn {Function File} {[@var{k}, @var{q1}, @var{p1}, @var{ee}, @var{er}] =} lqg (@var{sys}, @var{sigw}, @var{sigv}, @var{q}, @var{r}, @var{in_idx})
Design a linear-quadratic-gaussian optimal controller for the system
@example
dx/dt = A x + B u + G w       [w]=N(0,[Sigw 0    ])
    y = C x + v               [v]  (    0   Sigv ])
@end example
or
@example
x(k+1) = A x(k) + B u(k) + G w(k)   [w]=N(0,[Sigw 0    ])
  y(k) = C x(k) + v(k)              [v]  (    0   Sigv ])
@end example

@strong{Inputs}
@table @var
@item  sys
system data structure
@item  sigw
@itemx  sigv
intensities of independent Gaussian noise processes (as above)
@item  q
@itemx  r
state, control weighting respectively.  Control @acronym{ARE} is
@item  in_idx
names or indices of controlled inputs (see @command{sysidx}, @command{cellidx})

default: last dim(R) inputs are assumed to be controlled inputs, all
others are assumed to be noise inputs.
@end table
@strong{Outputs}
@table @var
@item    k
system data structure format @acronym{LQG} optimal controller (Obtain A, B, C
matrices with @command{sys2ss}, @command{sys2tf}, or @command{sys2zp} as
appropriate).
@item    p1
Solution of control (state feedback) algebraic Riccati equation.
@item    q1
Solution of estimation algebraic Riccati equation.
@item    ee
Estimator poles.
@item    es
Controller poles.
@end table
@seealso{h2syn, lqe, lqr}
@end deftypefn


@anchor{doc-lqr}
@deftypefn {Function File} {[@var{k}, @var{p}, @var{e}] =} lqr (@var{a}, @var{b}, @var{q}, @var{r}, @var{z})
construct the linear quadratic regulator for the continuous time system
@iftex
@tex
$$
 {dx\over dt} = A x + B u
$$
@end tex
@end iftex
@ifinfo

@example
dx
-- = A x + B u
dt
@end example

@end ifinfo
to minimize the cost functional
@iftex
@tex
$$
 J = \int_0^\infty x^T Q x + u^T R u
$$
@end tex
@end iftex
@ifinfo

@example
      infinity
      /
  J = |  x' Q x + u' R u
     /
    t=0
@end example
@end ifinfo

@noindent
@var{z} omitted or
@iftex
@tex
$$
 J = \int_0^\infty x^T Q x + u^T R u + 2 x^T Z u
$$
@end tex
@end iftex
@ifinfo

@example
      infinity
      /
  J = |  x' Q x + u' R u + 2 x' Z u
     /
    t=0
@end example

@end ifinfo
@var{z} included.

The following values are returned:

@table @var
@item k
The state feedback gain,
@iftex
@tex
$(A - B K)$
@end tex
@end iftex
@ifinfo
(@var{a} - @var{b}@var{k})
@end ifinfo
is stable and minimizes the cost functional

@item p
The stabilizing solution of appropriate algebraic Riccati equation.

@item e
The vector of the closed loop poles of
@iftex
@tex
$(A - B K)$.
@end tex
@end iftex
@ifinfo
(@var{a} - @var{b}@var{k}).
@end ifinfo
@end table

@strong{Reference}
Anderson and Moore, @cite{Optimal control: linear quadratic methods},
Prentice-Hall, 1990, pp. 56--58.
@end deftypefn


@anchor{doc-lsim}
@deftypefn {Function File} {[@var{y}, @var{x}] =} lsim (@var{sys}, @var{u}, @var{t}, @var{x0})
Produce output for a linear simulation of a system; produces 
a plot for the output of the system, @var{sys}.

@var{u} is an array that contains the system's inputs.  Each row in @var{u}
corresponds to a different time step.  Each column in @var{u} corresponds to a
different input.  @var{t} is an array that contains the time index of the
system; @var{t} should be regularly spaced.  If initial conditions are required
on the system, the @var{x0} vector should be added to the argument list.

When the lsim function is invoked a plot is not displayed; 
however, the data is returned in @var{y} (system output)
and @var{x} (system states).
@end deftypefn


@anchor{doc-place}
@deftypefn {Function File} {@var{K} =} place (@var{sys}, @var{p})
Computes the matrix @var{K} such that if the state
is feedback with gain @var{K}, then the eigenvalues  of the closed loop
system (i.e. @math{A-BK}) are those specified in the vector @var{p}.

Version: Beta (May-1997): If you have any comments, please let me know.
(see the file place.m for my address)
@end deftypefn


@node misc
@section Miscellaneous Functions (Not yet properly filed/documented)

@anchor{doc-axis2dlim}
@deftypefn {Function File} {} axis2dlim (@var{axdata})
Determine axis limits for 2-D data (column vectors); leaves a 10%
margin around the plots.
Inserts margins of +/- 0.1 if data is one-dimensional 
(or a single point).

@strong{Input}
@table @var
@item axdata
@var{n} by 2 matrix of data [@var{x}, @var{y}].
@end table

@strong{Output}
@table @var
@item axvec
Vector of axis limits appropriate for call to @command{axis} function.
@end table
@end deftypefn


@anchor{doc-moddemo}
@deftypefn {Function File} {} moddemo (@var{inputs})
Octave Control toolbox demo: Model Manipulations demo.
@end deftypefn


@anchor{doc-prompt}
@deftypefn {Function File} {} prompt (@var{str})
Prompt user to continue

@strong{Input}
@table @var
@item str
Input string. Its default value is: 
@example 
\n ---- Press a key to  continue ---
@end example
@end table
@end deftypefn


@anchor{doc-rldemo}
@deftypefn {Function File} {} rldemo (@var{inputs})
Octave Control toolbox demo: Root Locus demo.
@end deftypefn


@anchor{doc-rlocus}
@deftypefn {Function File} {[@var{rldata}, @var{k}] =} rlocus (@var{sys}[, @var{increment}, @var{min_k}, @var{max_k}])

Display root locus plot of the specified @acronym{SISO} system.
@example
@group
       -----   ---     --------
   --->| + |---|k|---->| SISO |----------->
       -----   ---     --------        |
       - ^                             |
         |_____________________________|
@end group
@end example

@strong{Inputs}
@table @var
@item sys
system data structure
@item min_k
Minimum value of @var{k}
@item max_k
Maximum value of @var{k}
@item increment
The increment used in computing gain values
@end table

@strong{Outputs}

Plots the root locus to the screen.
@table @var 
@item rldata
Data points plotted: in column 1 real values, in column 2 the imaginary values.
@item k
Gains for real axis break points.
@end table
@end deftypefn


@anchor{doc-sortcom}
@deftypefn {Function File} {[@var{yy}, @var{idx}] =} sortcom (@var{xx}[, @var{opt}])
Sort a complex vector.

@strong{Inputs}
@table @var
@item xx
Complex vector
@item opt
sorting option:
@table @code
@item "re"
Real part (default);
@item "mag"
By magnitude;
@item "im"
By imaginary part.
@end table
if @var{opt} is not chosen as @code{"im"}, then complex conjugate pairs are grouped together,
@math{a - jb} followed by @math{a + jb}.
@end table

@strong{Outputs}
@table @var
@item yy
Sorted values
@item idx
Permutation vector: @code{yy = xx(idx)}
@end table
@end deftypefn


@anchor{doc-ss2tf}
@deftypefn {Function File} {[@var{num}, @var{den}] =} ss2tf (@var{a}, @var{b}, @var{c}, @var{d})
Conversion from transfer function to state-space.
The state space system:
@iftex
@tex
$$ \dot x = Ax + Bu $$
$$ y = Cx + Du $$
@end tex
@end iftex
@ifinfo
@example
      .
      x = Ax + Bu
      y = Cx + Du
@end example
@end ifinfo

is converted to a transfer function:
@iftex
@tex
$$ G(s) = { { \rm num }(s) \over { \rm den }(s) } $$
@end tex
@end iftex
@ifinfo
@example

                num(s)
          G(s)=-------
                den(s)
@end example
@end ifinfo

used internally in system data structure format manipulations.
@end deftypefn


@anchor{doc-ss2zp}
@deftypefn {Function File} {[@var{pol}, @var{zer}, @var{k}] =} ss2zp (@var{a}, @var{b}, @var{c}, @var{d})
Converts a state space representation to a set of poles and zeros;
@var{k} is a gain associated with the zeros.

Used internally in system data structure format manipulations.
@end deftypefn


@anchor{doc-starp}
@deftypefn {Function File} {} starp (@var{P}, @var{K}, @var{ny}, @var{nu})

Redheffer star product or upper/lower LFT, respectively.
@example
@group

               +-------+
     --------->|       |--------->
               |   P   |
          +--->|       |---+  ny
          |    +-------+   |
          +-------------------+
                           |  |
          +----------------+  |
          |                   |
          |    +-------+      |
          +--->|       |------+ nu
               |   K   |
     --------->|       |--------->
               +-------+
@end group
@end example
If @var{ny} and @var{nu} ``consume'' all inputs and outputs of
@var{K} then the result is a lower fractional transformation. 
If @var{ny} and @var{nu} ``consume'' all inputs and outputs of 
@var{P} then the result is an upper fractional transformation.

@var{ny} and/or @var{nu} may be negative (i.e. negative feedback).
@end deftypefn


@anchor{doc-tf2ss}
@deftypefn {Function File} {[@var{a}, @var{b}, @var{c}, @var{d}] =} tf2ss (@var{num}, @var{den})
Conversion from transfer function to state-space.
The state space system:
@iftex
@tex
$$ \dot x = Ax + Bu $$
$$ y = Cx + Du $$
@end tex
@end iftex
@ifinfo
@example
      .
      x = Ax + Bu
      y = Cx + Du
@end example
@end ifinfo
is obtained from a transfer function:
@iftex
@tex
$$ G(s) = { { \rm num }(s) \over { \rm den }(s) } $$
@end tex
@end iftex
@ifinfo
@example
                num(s)
          G(s)=-------
                den(s)
@end example
@end ifinfo

The vector @var{den} must contain only one row, whereas the vector 
@var{num} may contain as many rows as there are outputs @var{y} of 
the system. The state space system matrices obtained from this function 
will be in controllable canonical form as described in @cite{Modern Control 
Theory}, (Brogan, 1991).
@end deftypefn


@anchor{doc-tf2zp}
@deftypefn {Function File} {[@var{zer}, @var{pol}, @var{k}] =} tf2zp (@var{num}, @var{den})
Converts transfer functions to poles-and-zero representations.

Returns the zeros and poles of the @acronym{SISO} system defined 
by @var{num}/@var{den}.
@var{k} is a gain associated with the system zeros.
@end deftypefn


@anchor{doc-zp2ss}
@deftypefn {Function File} {[@var{a}, @var{b}, @var{c}, @var{d}] =} zp2ss (@var{zer}, @var{pol}, @var{k})
Conversion from zero / pole to state space.

@strong{Inputs}
@table @var
@item zer
@itemx pol
Vectors of (possibly) complex poles and zeros of a transfer
function. Complex values must come in conjugate pairs
(i.e., @math{x+jy} in @var{zer} means that @math{x-jy} is also in @var{zer}).
The number of zeros must not exceed the number of poles.
@item k
Real scalar (leading coefficient).
@end table

@strong{Outputs}
@table @var
@item @var{a}
@itemx @var{b}
@itemx @var{c}
@itemx @var{d}
The state space system, in the form:
@iftex
@tex
$$ \dot x = Ax + Bu $$
$$ y = Cx + Du $$
@end tex
@end iftex
@ifinfo
@example
     .
     x = Ax + Bu
     y = Cx + Du
@end example
@end ifinfo
@end table
@end deftypefn


@anchor{doc-zp2tf}
@deftypefn {Function File} {[@var{num}, @var{den}] =} zp2tf (@var{zer}, @var{pol}, @var{k})
Converts zeros / poles to a transfer function.

@strong{Inputs}
@table @var
@item zer
@itemx pol
Vectors of (possibly complex) poles and zeros of a transfer
function.  Complex values must appear in conjugate pairs.
@item k
Real scalar (leading coefficient).
@end table
@end deftypefn


