/*

Copyright (C) 2000, 2001, 2004, 2005, 2006, 2007, 2008 Gabriele Pannocchia

This file is part of Octave.

Octave is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3 of the License, or (at your
option) any later version.

Octave is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with Octave; see the file COPYING.  If not, see
<http://www.gnu.org/licenses/>.

*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <cfloat>

#include "dbleCHOL.h"
#include "dbleSVD.h"
#include "mx-m-dm.h"
#include "EIG.h"

#include "defun-dld.h"
#include "error.h"
#include "gripes.h"
#include "oct-obj.h"
#include "pr-output.h"
#include "utils.h"

static Matrix
null (const Matrix& A, octave_idx_type& rank)
{
  Matrix retval;

  rank = 0;

  if (! A.is_empty ())
    {
      SVD A_svd (A);

      DiagMatrix S = A_svd.singular_values ();

      ColumnVector s = S.diag ();

      Matrix V = A_svd.right_singular_matrix ();

      octave_idx_type A_nr = A.rows ();
      octave_idx_type A_nc = A.cols ();

      octave_idx_type tmp = A_nr > A_nc ? A_nr : A_nc;

      double tol = tmp * s(0) * DBL_EPSILON;

      octave_idx_type n = s.length ();

      for (octave_idx_type i = 0; i < n; i++)
	{
	  if (s(i) > tol)
	    rank++;
	}

      if (rank < A_nc)
	retval = V.extract (0, rank, A_nc-1, A_nc-1);
      else
	retval.resize (A_nc, 0);

      for (octave_idx_type i = 0; i < retval.numel (); i++)
	if (std::abs (retval(i)) < DBL_EPSILON)
	  retval(i) = 0;
    }

  return retval;
}

static int
qp (const Matrix& H, const ColumnVector& q,
    const Matrix& Aeq, const ColumnVector& beq,
    const Matrix& Ain, const ColumnVector& bin,
    int maxit,
    ColumnVector& x, ColumnVector& lambda, int& iter)
{
  int info = 0;

  iter = 0;

  double rtol = sqrt (DBL_EPSILON);

  // Problem dimension.
  octave_idx_type n = x.length ();

  // Dimension of constraints.
  octave_idx_type n_eq = beq.length ();
  octave_idx_type n_in = bin.length ();

  // Filling the current active set.

  octave_idx_type n_act = n_eq;

  octave_idx_type n_tot = n_eq + n_in;

  // Equality constraints come first.  We won't check the sign of the
  // Lagrange multiplier for those.

  Matrix Aact = Aeq;
  ColumnVector bact = beq;
  ColumnVector Wact;

  if (n_in > 0)
    {
      ColumnVector res = Ain*x - bin;

      for (octave_idx_type i = 0; i < n_in; i++)
	{
	  res(i) /= (1.0 + std::abs (bin(i)));

	  if (res(i) < rtol)
	    {
	      n_act++;
	      Aact = Aact.stack (Ain.row (i));
	      bact.resize (n_act, bin(i));
	      Wact.resize (n_act-n_eq, i);
	    }
	}
    }

  // Computing the ???

  EIG eigH (H);

  if (error_state)
    {
      error ("qp: failed to compute eigenvalues of H");
      return -1;
    }

  ColumnVector eigenvalH = real (eigH.eigenvalues ());
  Matrix eigenvecH = real (eigH.eigenvectors ());
  double minReal = eigenvalH.min ();
  octave_idx_type indminR = 0;
  for (octave_idx_type i = 0; i < n; i++)
    {
      if (minReal == eigenvalH(i))
	{
	  indminR = i;
	  break;
	}
    }

  bool done = false;

  double alpha = 0.0;

  Matrix R;
  Matrix Y (n, 0, 0.0);

  ColumnVector g (n, 0.0);
  ColumnVector p (n, 0.0);

  ColumnVector lambda_tmp (n_in, 0.0);

  while (! done)
    {
      iter++;

      // Current Gradient
      // g = q + H * x;

      g = q + H * x;

      if (n_act == 0)
	{
	  // There are no active constraints.

	  if (minReal > 0.0)
	    {
	      // Inverting the Hessian.  Using the Cholesky
	      // factorization since the Hessian is positive
	      // definite.

	      CHOL cholH (H);

	      R = cholH.chol_matrix ();

	      Matrix Hinv = chol2inv (R);

	      // Computing the unconstrained step.
	      // p = -Hinv * g;

	      p = -Hinv * g;

	      info = 0;
	    }
	  else
	    {
	      // Finding the negative curvature of H.

	      p = eigenvecH.column (indminR);

	      // Following the negative curvature of H.

	      if (p.transpose () * g > DBL_EPSILON)
	        p = -p;

	      info = 1;
	    }

	  // Multipliers are zero.
          lambda_tmp.fill (0.0);
	}
      else
        {
	  // There are active constraints.

	  // Computing the null space.

	  octave_idx_type rank;

	  Matrix Z = null (Aact, rank);

	  octave_idx_type dimZ = n - rank;

	  // FIXME -- still remain to handle the case of
	  // non-full rank active set matrix.

	  // Computing the Y matrix (orthogonal to Z)
	  Y = Aact.pseudo_inverse ();

	  // Reduced Hessian
	  Matrix Zt = Z.transpose ();
	  Matrix rH = Zt * H * Z;

	  octave_idx_type pR = 0;

	  if (dimZ > 0)
	    {
	      // Computing the Cholesky factorization (pR = 0 means
	      // that the reduced Hessian was positive definite).

	      CHOL cholrH (rH, pR);
	      Matrix tR = cholrH.chol_matrix ();
	      if (pR == 0)
		R = tR;
	    }

	  if (pR == 0)
	    {
	      info = 0;

	      // Computing the step pz. 
	      if (dimZ > 0)
		{
		  // Using the Cholesky factorization to invert rH

		  Matrix rHinv = chol2inv (R);

		  ColumnVector pz = -rHinv * Zt * g;

		  // Global step.
		  p = Z * pz;
		}
	      else
		{
		  // Global step.
		  p.fill (0.0);
		}
	    }
	  else
	    {
	      info = 1;

	      // Searching for the most negative curvature.

	      EIG eigrH (rH);

	      if (error_state)
		{
		  error ("qp: failed to compute eigenvalues of rH");
		  return -1;
		}

	      ColumnVector eigenvalrH = real (eigrH.eigenvalues ());
	      Matrix eigenvecrH = real (eigrH.eigenvectors ());
	      double mRrH = eigenvalrH.min ();
	      indminR = 0;
	      for (octave_idx_type i = 0; i < n; i++)
		{
		  if (mRrH == eigenvalH(i))
		    {
		      indminR = i;
		      break;
		    }
		}

	      ColumnVector eVrH = eigenvecrH.column (indminR);

	      // Computing the step pz.
	      p = Z * eVrH;

	      if (p.transpose () * g > DBL_EPSILON)
		p = -p;
	    }
	}

      // Checking the step-size.
      ColumnVector abs_p (n);
      for (octave_idx_type i = 0; i < n; i++)
	abs_p(i) = std::abs (p(i));
      double max_p = abs_p.max ();

      if (max_p < rtol)
	{
	  // The step is null.  Checking constraints.
	  if (n_act - n_eq == 0)
	    // Solution is found because no inequality
	    // constraints are active.
	    done = true;
	  else
	    {
	      // Computing the multipliers only for the inequality
	      // constraints that are active.  We do NOT compute
	      // multipliers for the equality constraints.
	      Matrix Yt = Y.transpose ();
	      Yt = Yt.extract_n (n_eq, 0, n_act-n_eq, n);
	      lambda_tmp = Yt * (g + H * p);

	      // Checking the multipliers.  We remove the most
	      // negative from the set (if any).
	      double min_lambda = lambda_tmp.min ();
	      if (min_lambda >= 0)
		{
		  // Solution is found.
		  done = true;
		}
	      else
		{
		  octave_idx_type which_eig = 0;
		  for (octave_idx_type i = 0; i < n_act; i++)
		    {
		      if (lambda_tmp(i) == min_lambda)
			{
			  which_eig = i;
			  break;
			}
		    }

		  // At least one multiplier is negative, we
		  // remove it from the set.

		  n_act--;
		  for (octave_idx_type i = which_eig; i < n_act - n_eq; i++)
		    {
		      Wact(i) = Wact(i+1);
		      for (octave_idx_type j = 0; j < n; j++)
			Aact(n_eq+i,j) = Aact(n_eq+i+1,j);
		      bact(n_eq+i) = bact(n_eq+i+1);
		    }

		  // Resizing the active set.
		  Wact.resize (n_act-n_eq);
		  bact.resize (n_act);
		  Aact.resize (n_act, n);
		}
	    }
	}
      else
	{
	  // The step is not null.
	  if (n_act - n_eq == n_in)
	    {
	      // All inequality constraints were active.  We can
	      // add the whole step.
	      x += p;
	    }
	  else
	    {
	      // Some constraints were not active.  Checking if
	      // there is a blocking constraint.
	      alpha = 1.0;
	      octave_idx_type is_block = -1;

	      for (octave_idx_type i = 0; i < n_in; i++)
		{
		  bool found = false;

		  for (octave_idx_type j = 0; j < n_act-n_eq; j++)
		    {
		      if (Wact(j) == i)
			{
			  found = true;
			  break;
			}
		    }

		  if (! found)
		    {
		      // The i-th constraint was not in the set.  Is it a
		      // blocking constraint?

		      RowVector tmp_row = Ain.row (i);
		      double tmp = tmp_row * p;
		      double res = tmp_row * x;

		      if (tmp < 0.0)
		        {
			  double alpha_tmp = (bin(i) - res) / tmp;

			  if (alpha_tmp < alpha)
			    {
			      alpha = alpha_tmp;
			      is_block = i;
			    }
			}
		    }
		}

	      // In is_block there is the index of the blocking
	      // constraint (if any).
	      if (is_block >= 0)
		{
		  // There is a blocking constraint (index in
		  // is_block) which is added to the active set.
		  n_act++;
		  Aact = Aact.stack (Ain.row (is_block));
		  bact.resize (n_act, bin(is_block));
		  Wact.resize (n_act-n_eq, is_block);

		  // Adding the reduced step
		  x += alpha * p;
		}
	      else
		{
		  // There are no blocking constraints.  Adding the
		  // whole step.
		  x += alpha * p;
		}
	    }
	}

      if (iter == maxit)
	{
	  done = true;
	  // warning ("qp_main: maximum number of iteration reached");
	  info = 3;
	}
    }

  lambda_tmp = Y.transpose () * (g + H * p);

  // Reordering the Lagrange multipliers.

  lambda.resize (n_tot);
  lambda.fill (0.0);
  for (octave_idx_type i = 0; i < n_eq; i++)
    lambda(i) = lambda_tmp(i);

  for (octave_idx_type i = n_eq; i < n_tot; i++)
    {
      for (octave_idx_type j = 0; j < n_act-n_eq; j++)
	{
	  if (Wact(j) == i - n_eq)
	    {
	      lambda(i) = lambda_tmp(n_eq+j);
	      break;
	    }
	}
    }

  return info;
}

DEFUN_DLD (__qp__, args, ,
  "-*- texinfo -*-\n\
@deftypefn {Loadable Function} {[@var{x}, @var{lambda}, @var{info}, @var{iter}] =} __qp__ (@var{x0}, @var{H}, @var{q}, @var{Aeq}, @var{beq}, @var{Ain}, @var{bin}, @var{maxit})\n\
Undocumented internal function.\n\
@end deftypefn")
{
  octave_value_list retval;

  if (args.length () == 8)
    {
      const ColumnVector x0  (args(0) . vector_value ());
      const Matrix H         (args(1) . matrix_value ());
      const ColumnVector q   (args(2) . vector_value ());
      const Matrix Aeq       (args(3) . matrix_value ());
      const ColumnVector beq (args(4) . vector_value ());
      const Matrix Ain       (args(5) . matrix_value ());
      const ColumnVector bin (args(6) . vector_value ());
      const int maxit        (args(7) . int_value ());

      if (! error_state)
	{
	  int iter = 0;

	  // Copying the initial guess in the working variable
	  ColumnVector x = x0;

	  // Reordering the Lagrange multipliers
	  ColumnVector lambda;

	  int info = qp (H, q, Aeq, beq, Ain, bin, maxit, x, lambda, iter);

	  if (! error_state)
	    {
	      retval(3) = iter;
	      retval(2) = info;
	      retval(1) = lambda;
	      retval(0) = x;
	    }
	  else
	    error ("qp: internal error");
	}
      else
	error ("__qp__: invalid arguments");
    }
  else
    print_usage ();

  return retval;
}
