Home > MRFLearning > MLgrid.m

MLgrid

PURPOSE ^

Estimate the ML parameters for a rectangular grid boltzmann m/c,

SYNOPSIS ^

function [model] = MLgrid(data,R,C)

DESCRIPTION ^

 Estimate the ML parameters for a rectangular grid boltzmann m/c,
 using the junction tree algorithm for exact inference
 Inputs:
           data : (#samples X #nodes) matrix containing training samples
                  Each node can take values from {+1,-1} or {0,1}
            R    : # rows in the grid
           C    : # columns in the grid
 Returns:
           model: struct with fields
                  numRows: R
                  numCols: C
                  alpha  : (R X C) matrix of node biases (ML estimates)
                  wHor   : (R X C-1) matrix of horizontal edge weights (ML estimates)
                  wVer   : (R-1 X C) matrix of vertical edge weights (ML estimates)
           Optionally saves a file "paramVec.mat" showing the sequence of updates to the parameters 

 The node value representation ( +1/-1 or 0/1) intended by the user is guessed from the training samples.       
 If using -1/+1, the data is first mapped to 0/1 and the model params are learned. 
 These learned params are then mapped back to the -1/1 case.
 
 If the variable MONITOR is set to 1 on line <51>, a file "paramVec.mat" is generated that saves the parameter
 updates. One can plot these values to see if the gradient learning
 parmeters (MAX_ITERATIONS, EPSILON1, rho) are reasonable. If not they can
 be changed on lines <48-50>

 Stopping criterion for gradient ascent: at each iteration, the learning rate (rho) is increased if log-likelihood increases (rho=1.1*rho)
 and decreased otherwise (rho=0.5*rho). Stops when either MAX_ITERATIONS
 is reached or maximum change across all parameters is less than EPSILON1

CROSS-REFERENCE INFORMATION ^

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