bham.leakiest.infotheory

Class BlahutArimoto

java.lang.Object

bham.leakiest.infotheory.BlahutArimoto

public class BlahutArimoto
extends java.lang.Object

This class calculates the capacity of a channel using the Blahut-Arimoto Algorithm. The description for this algorithm is largely taken from the paper: "A Generalized Blahut-Arimoto Algorithm" by Pascal Vontobel", N.B. this paper uses natural logs and e where as we are using log2 and 2, to give the capacity in bit.

Version:

1.2.5

Author:

Tom Chothia, Yusuke Kawamoto

Constructor Summary

Constructors

Constructor and Description
BlahutArimoto(Channel channel, double[] inputPMF_Q, double acceptableError, int noOfiterations) Sets initial data to calculates the capacity.
BlahutArimoto(Channel channel, double acceptableError, int noOfiterations) Sets initial data to calculates the capacity.
BlahutArimoto(java.lang.String[] inputNames, java.lang.String[] outputNames, double[][] channelMatrix_W, double[] inputPMF_Q, double acceptableError, int noOfiterations) Sets initial data to calculates the capacity.

Method Summary

Modifier and Type	Method and Description
double	calculateCapacity() Calculates capacity.
double	calculateError(double[] inputProbs_Q, double[][] matrix_W) Finds the maximum possible error for a input PMF using: I(Q,W) ≤ true Cap ≤ max_x[T(x) -log(Q(x))] i.e.
double	getAcceptableError() Returns the acceptable error of the result.
double	getCapacity() Returns the capacity.
int	getIterationCount() Returns the number of iterations in Blahut-Arimoto algorithm.
double[]	getMaxInputDist() Returns the input distribution that achieves capacity.
double	getPossibleError() Returns the possible error of the result.
void	setVerbose(boolean b) Sets the value of verbose.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BlahutArimoto

public BlahutArimoto(Channel channel,
                     double[] inputPMF_Q,
                     double acceptableError,
                     int noOfiterations)

Sets initial data to calculates the capacity.

Parameters:

channel - channel

inputPMF_Q - input PMF array

acceptableError - acceptable error rate for the calculation of capacity

noOfiterations - the maximum number of iterations to calculate of capacity

BlahutArimoto

public BlahutArimoto(Channel channel,
                     double acceptableError,
                     int noOfiterations)

Sets initial data to calculates the capacity.

Parameters:

channel - channel

acceptableError - acceptable error rate for the calculation of capacity

noOfiterations - the maximum number of iterations to calculate of capacity

BlahutArimoto

public BlahutArimoto(java.lang.String[] inputNames,
                     java.lang.String[] outputNames,
                     double[][] channelMatrix_W,
                     double[] inputPMF_Q,
                     double acceptableError,
                     int noOfiterations)

Sets initial data to calculates the capacity.

Parameters:

inputNames - input names

outputNames - output names

channelMatrix_W - channel matrix

inputPMF_Q - input PMF array

acceptableError - acceptable error rate for the calculation of capacity

noOfiterations - the maximum number of iterations to calculate of capacity

Method Detail

calculateCapacity

public double calculateCapacity()

Calculates capacity.

Returns:

capacity

calculateError

public double calculateError(double[] inputProbs_Q,
                             double[][] matrix_W)

Finds the maximum possible error for a input PMF using:
I(Q,W) ≤ true Cap ≤ max_x[T(x) -log(Q(x))] i.e. max possible err is max_x[T(x) -log(Q(x))] - I(Q,W).
Find max_x[T(x) -log(Q(x))] where
T(x) = Sigma_y W(y|x).log(Q(x).W(y|x) / (QW)(y))
we take log (0/0) = 0 (as x/x → 1 as x → 0 and log(1) = 0) and n.log 0 = -inf (as n.log(x) → -inf as x → x)

Parameters:

inputProbs_Q - input PMF

matrix_W - channel matrix

Returns:

the maximum possible error

getAcceptableError

public double getAcceptableError()

Returns the acceptable error of the result.

Returns:

acceptable error

getCapacity

public double getCapacity()

Returns the capacity.

Returns:

capacity

getIterationCount

public int getIterationCount()

Returns the number of iterations in Blahut-Arimoto algorithm.

Returns:

the number of iterations

getMaxInputDist

public double[] getMaxInputDist()

Returns the input distribution that achieves capacity.

Returns:

maximising input distribution

getPossibleError

public double getPossibleError()

Returns the possible error of the result.

Returns:

possible error

setVerbose

public void setVerbose(boolean b)

Sets the value of verbose.

Parameters:

b - the value of verbose