marginalization.m

Duda的《模式分类》第二版的配套的Matlab源代码

function [targets, P] = Marginalization(patterns, targets, params, plot_on)

% Classify data with missing features using the marginal distribution
%
% Inputs:
% 	patterns    - Input patterns
%	targets	    - Input targets
%	params      - [The number of the missing feature, Number of patterns with which to compute the marginal]
%   plot_on     - Unused
%
% Outputs
%   targets     - Output targets
%	P           - P(w|x) (Probability of a class given the good features)

warning off;

[missing, N] = process_params(params);

train_patterns = patterns(:,1:N);
train_targets  = targets(1:N);

[d, L] = size(train_patterns);

if (missing > d),
    error(['The number of the missing pattern must be between 1 and ' num2str(d)])
end

not_missing = find(~ismember(1:d, missing));

%Calculate the marginal distribution using histograms
Nbins           = max(3,floor(size(train_patterns,2).^(1/3)));
[p, b, region]  = high_histogram(train_patterns,Nbins);
classes         = unique(train_targets);

Ptrain = zeros(length(classes), Nbins^(d-1));
for i = 1:length(classes),
    indices	    = find(train_targets == classes(i));
    g_i         = high_histogram(train_patterns(:,indices),Nbins,region);
    Pc          = squeeze(sum(g_i.*p,missing)./sum(p,missing));
    bad         = find(~isfinite(Pc));
    Pc(bad)     = 0;
    Ptrain(i,:) = Pc(:)';
end
if (d > 2)
    Ptrain = reshape(Ptrain, [length(classes) ones(1,d-1)*d]);
end

% Classify the marginal probabilities for all the patterns
[temp, binned_patterns] = high_histogram(patterns, Nbins, region);

P   = zeros(length(classes), size(patterns,2));
for i = 1:size(P,2),
    s = ':,';
    for j = 1:d-1,
        s = [s, num2str(binned_patterns(not_missing(j),i))];
        if (j ~= d-1)
            s = [s, ','];
        end
    end
    s = [s, ''];
    P(:,i) = eval(['Ptrain(', s, ')']); 
end