72 lines
2.7 KiB
Matlab
72 lines
2.7 KiB
Matlab
% implements Bayes_Learning, returns the outputs (p1: learned Bernoulli
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% parameters of the first class, p2: learned Bernoulli parameters of the
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% second class, pc1: best prior of the first class, pc2: best prior of the
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% second class
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function [p1,p2,pc1,pc2] = Bayes_Learning(training_data, validation_data)
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[train_row_size, column_size] = size (training_data); % dimension of training data
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[valid_row_size, ~] = size (validation_data); % dimension of validation data
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X = training_data(1:train_row_size, 1:column_size-1); %Training data
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y = training_data(:,column_size); % training labels
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Xvalid = validation_data(1:valid_row_size, 1:column_size-1); %Training data
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yvalid = validation_data(:,column_size); % training labels
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% (1) TODO: find label counts of class 1 and class 2
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% (2) TODO: get MLE p1, p2
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[p1,p2] = MLE_Learning(training_data);
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% Use different P(C_1) and P(C_2) on validation set
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% We compute g(x) = based on priors P(C_1), P(C_2), MLE estimator p1, p2, and x_{1*D}
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error_table = zeros(11,4); % build an error table with 4 columns of : sigma, P(C1), P(C2), error_rate
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index = 1; % row index of error table
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for sigma = [0.00001,0.0001,0.001,0.01,0.1,1,2,3,4,5,6]
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P_C1 = 1-(exp(-sigma)); % set priors using formula P(C1)=1-(exp(-sigma))
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P_C2 = 1 - P_C1;
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error_count = 0; % total number of errors to be count
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% (3) TODO: compute likelihood for class1 and class2 , then compute the posterior
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% probability for both classes (posterior = prior x likelihood).
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for i = 1:valid_row_size
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x = Xvalid(i, :);
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correct_label = yvalid(i);
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postc1 = prod(p1 .^ x .* (1 - p1) .^ (1 - x)) * P_C1;
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postc2 = prod(p2 .^ x .* (1 - p2) .^ (1 - x)) * P_C2;
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% Classify each validation sample as whichever class has the higher posterior probability.
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if postc1 > postc2
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lab = 1;
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else
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lab = 2;
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end
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% If the sample is misclassified, increment the error count (error_count = error_count + 1);
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if lab ~= correct_label
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error_count = error_count + 1;
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end
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end
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error_table(index,1) = sigma;
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error_table(index,2) = P_C1;
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error_table(index,3) = P_C2;
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error_table(index,4) = error_count/valid_row_size; % update error table
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index = index + 1;
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end
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% get the best priors
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[~, I] = min(error_table(:,4)); % find row index of the lowest error rate on validation set
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pc1 = error_table(I,2);
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pc2 = error_table(I,3); % best priors
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% print error table to terminal
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fprintf('\n Error rates of all priors on validation set: \n\n');
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fprintf(' sigma P(C1) P(C2) error rate on validation set\n\n');
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disp(error_table);
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end |