org.knowceans.sandbox.gauss
Class GmmGibbsSampler2

java.lang.Object
  org.knowceans.sandbox.gauss.GmmGibbsSampler2

public class GmmGibbsSampler2
extends java.lang.Object

GmmGibbsSampler tests a simple Gibbs sampler that simulates the posterior of a Gaussian mixture model, i.e., the parameter distribution as a function of the evidence. Adapted from http://www.sph.umich.edu/csg/abecasis/class/815.23.pdf .

Sample each of the mixture parameters from conditional distribution: Dirichlet, Normal and Gamma distributions are typical.

Simple alternative is to sample the origin of each observation and assign observation to specific component (used here).

Author:

heinrich

Field Summary

private static int	BURN_IN burn-in period
(package private) double[]	data
private static int	ITERATIONS max iterations
private static double	MIN_GROUP minimum members of a group
private static int	THIN_INTERVAL sampling lag (?)

Constructor Summary

GmmGibbsSampler2(double[] data)
Initialise the Gibbs sampler with data.

Method Summary

(package private) void	addObservation(double x, int group, double[] counts, double[] sum, double[] sumsq) For updating mixture parameters
void	configure(int iterations, int burnIn, int minGroup, int thinInterval)
private void	gibbs(int k, double[] probs, double[] mean, double[] sigma) Main method: Select initial state ?
(package private) void	initialState(int k, int[] group, double[] counts, double[] sum, double[] sumsq) Initialisation: Must start with an assignment of observations to groupings ?
static void	main(java.lang.String[] args) Driver with example data.
(package private) void	removeObservation(double x, int group, double[] counts, double[] sum, double[] sumsq) For updating mixture parameters
(package private) int	sampleGroup(double x, int k, double[] probs, double[] mean, double[] sigma) Sampling a component, P(z_j=i | z_-j, x_j, theta) = pi_i * f(x_j | theta_j) / sum_m pi_m f(x_j | theta_m) Calculate the probability that the observation originated from each component.
(package private) void	updateEstimates(int k, int n, double[] prob, double[] mean, double[] sigma, double[] counts, double[] sum, double[] sumsq) Update the parameters.

Methods inherited from class java.lang.Object

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

Field Detail

data

double[] data

MIN_GROUP

private static double MIN_GROUP

minimum members of a group

THIN_INTERVAL

private static int THIN_INTERVAL

sampling lag (?)

BURN_IN

private static int BURN_IN

burn-in period

ITERATIONS

private static int ITERATIONS

max iterations

Constructor Detail

GmmGibbsSampler2

public GmmGibbsSampler2(double[] data)

Initialise the Gibbs sampler with data.

Parameters:

data -

Method Detail

updateEstimates

void updateEstimates(int k,
                     int n,
                     double[] prob,
                     double[] mean,
                     double[] sigma,
                     double[] counts,
                     double[] sum,
                     double[] sumsq)

Update the parameters. Before sampling a new origin for an observation, update mixture parameters given current assignments. Could be expensive!

Parameters:

k -

n -

prob -

mean -

sigma -

counts -

sum -

sumsq -

sampleGroup

int sampleGroup(double x,
                int k,
                double[] probs,
                double[] mean,
                double[] sigma)

Sampling a component, P(z_j=i | z_-j, x_j, theta) = pi_i * f(x_j | theta_j) / sum_m pi_m f(x_j | theta_m)

Calculate the probability that the observation originated from each component. Use random number(s) to assign component membership.

Parameters:

x -

k -

probs -

mean -

sigma -

Returns:

removeObservation

void removeObservation(double x,
                       int group,
                       double[] counts,
                       double[] sum,
                       double[] sumsq)

For updating mixture parameters

Parameters:

x -

group -

counts -

sum -

sumsq -

addObservation

void addObservation(double x,
                    int group,
                    double[] counts,
                    double[] sum,
                    double[] sumsq)

For updating mixture parameters

Parameters:

x -

group -

counts -

sum -

sumsq -

initialState

void initialState(int k,
                  int[] group,
                  double[] counts,
                  double[] sum,
                  double[] sumsq)

Initialisation: Must start with an assignment of observations to groupings ? Many alternatives are possible, I chose to perform random assignments with equal probabilities�

Parameters:

k -

group -

counts -

sum -

sumsq -

gibbs

private void gibbs(int k,
                   double[] probs,
                   double[] mean,
                   double[] sigma)

Main method: Select initial state ? Repeat a large number of times: 1. Select an element 2. Update conditional on other elements. If appropriate, output summary for each run.

Parameters:

k -

probs -

mean -

sigma -

configure

public void configure(int iterations,
                      int burnIn,
                      int minGroup,
                      int thinInterval)

main

public static void main(java.lang.String[] args)

Driver with example data.

Parameters:

args -