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## cern.jet.random
Class ChiSquare

    java.lang.Object
      cern.colt.PersistentObject
          cern.jet.random.AbstractDistribution
              cern.jet.random.AbstractContinousDistribution
                  cern.jet.random.ChiSquare

All Implemented Interfaces:
  Cloneable, DoubleFunction, IntFunction, Serializable

public class ChiSquare
extends AbstractContinousDistribution

ChiSquare distribution; See the math definition and animated definition.

A special case of the Gamma distribution.

`p(x) = (1/g(f/2)) * (x/2)^(f/2-1) * exp(-x/2)` with `g(a)` being the gamma function and `f` being the degrees of freedom.

Valid parameter ranges: `freedom > 0`.

Instance methods operate on a user supplied uniform random number generator; they are unsynchronized.

Static methods operate on a default uniform random number generator; they are synchronized.

Implementation:

Method: Ratio of Uniforms with shift.
High performance implementation. This is a port of RandChiSquare used in CLHEP 1.4.0 (C++). CLHEP's implementation, in turn, is based on `chru.c` from the C-RAND / WIN-RAND library. C-RAND's implementation, in turn, is based upon

J.F. Monahan (1987): An algorithm for generating chi random variables, ACM Trans. Math. Software 13, 168-172.

Version:
  1.0, 09/24/99
See Also:
  Serialized Form

Field Summary

Fields inherited from class cern.colt.PersistentObject
`serialVersionUID`

Constructor Summary
`ChiSquare(double freedom, RandomEngine randomGenerator)` Constructs a ChiSquare distribution.

Method Summary
`double` | `cdf(double x)` Returns the cumulative distribution function.
`double` | `nextDouble()` Returns a random number from the distribution.
`double` | `nextDouble(double freedom)` Returns a random number from the distribution; bypasses the internal state.
`double` | `pdf(double x)` Returns the probability distribution function.
`void` | `setState(double freedom)` Sets the distribution parameter.
`static double` | `staticNextDouble(double freedom)` Returns a random number from the distribution.
`String` | `toString()` Returns a String representation of the receiver.

Methods inherited from class cern.jet.random.AbstractDistribution
`apply, apply, clone, makeDefaultGenerator, nextInt`

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Constructor Detail

### ChiSquare

    public ChiSquare(double freedom,
                     RandomEngine randomGenerator)

  Constructs a ChiSquare distribution. Example: freedom=1.0.

Parameters:
  `freedom` - degrees of freedom.
Throws:
  `IllegalArgumentException` - if `freedom < 1.0`.

Method Detail

### cdf

    public double cdf(double x)

  Returns the cumulative distribution function.

### nextDouble

    public double nextDouble()

  Returns a random number from the distribution.

  Specified by:
    `nextDouble` in class `AbstractDistribution`

### nextDouble

    public double nextDouble(double freedom)

  Returns a random number from the distribution; bypasses the internal state.

  Parameters:
    `freedom` - degrees of freedom. It should hold `freedom < 1.0`.

### pdf

    public double pdf(double x)

  Returns the probability distribution function.

### setState

    public void setState(double freedom)

  Sets the distribution parameter.

  Parameters:
    `freedom` - degrees of freedom.
  Throws:
    `IllegalArgumentException` - if `freedom < 1.0`.

### staticNextDouble

    public static double staticNextDouble(double freedom)

  Returns a random number from the distribution.

  Parameters:
    `freedom` - degrees of freedom.
  Throws:
    `IllegalArgumentException` - if `freedom < 1.0`.

### toString

    public String toString()

  Returns a String representation of the receiver.

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