adaboost_tr.m

boost算法

function adaboost_model = ADABOOST_tr(tr_func_handle, te_func_handle, train_set, labels, no_of_hypothesis)
%
% ADABOOST TRAINING: A META-LEARNING ALGORITHM
%  adaboost_model = ADABOOST_tr(tr_func_handle,te_func_handle,
%                               train_set,labels,no_of_hypothesis)
% 
%        'tr_func_handle' and 'te_func_handle' are function handles for
%        training and testing of a weak learner, respectively. The weak learner
%        has to support the learning in weighted datasets. The prototypes
%        of these functions has to be as follows.
%
%        model = train_func(train_set,sample_weights,labels)
%                    train_set: a TxD-matrix where each row is a training sample in
%                        a D dimensional feature space.
%                    sample_weights: a Tx1 dimensional vector, the i-th entry 
%                        of which denotes the weight of the i-th sample.
%                    labels: a Tx1 dimensional vector, the i-th entry of which
%                        is the label of the i-th sample.
%                    model: the output model of the training phase, which can 
%                        consists of parameters estimated.
%
%        [L,hits,error_rate] = test_func(model,test_set,sample_weights,true_labels)
%                    model: the output of train_func
%                    test_set: a KxD dimensional matrix, each of whose row is a
%                        testing sample in a D dimensional feature space.
%                    sample_weights:  a Dx1 dimensional vector, the i-th entry 
%                        of which denotes the weight of the i-th sample.
%                    true_labels: a Dx1 dimensional vector, the i-th entry of which
%                        is the label of the i-th sample.
%                    L: a Dx1-array with the predicted labels of the samples.
%                    hits: number of hits, calculated with the comparison of L and
%                        true_labels.
%                    error_rate: number of misses divided by the number of samples.
%        
%
%        'train_set' contains the samples for training and it is NxD matrix
%        where N is the number of samples and D is the dimension of the
%        feature space. 'labels' is an Nx1 matrix containing the class
%        labels of the samples. 'no_of_hypothesis' is the number of weak
%        learners to be used.
%
%        The output 'adaboost_model' is a structure with the fields 
%         - 'weights': 1x'no_of_hypothesis' matrix specifying the weights
%                      of the resulted weighted majority voting combination 
%         - 'parameters': 1x'no_of_hypothesis' structure matrix specifying
%                         the special parameters of the hypothesis that is
%                         created at the corresponding iteration of 
%                         learning algorithm
% 
%        Specific Properties That Must Be Satisfied by The Function pointed
%        by 'func_handle'
%        ------------------------------------------------------------------
%
% Note: Labels must be positive integers from 1 upto the number of classes.
% Node-2: Weighting is done as specified in AIMA book, Stuart Russell et.al. (sec edition)
%
% Bug Reporting: Please contact the author for bug reporting and comments.
%
% Cuneyt Mertayak
% email: [e-mail]
% version: 1.0
% date: 21/05/2007
%

adaboost_model = struct('weights',zeros(1,no_of_hypothesis),...
						'parameters',[]); %cell(1,no_of_hypothesis));

sample_n = size(train_set,1);
samples_weight = ones(sample_n,1)/sample_n;

for turn=1:no_of_hypothesis
	adaboost_model.parameters{turn} = tr_func_handle(train_set,samples_weight,labels);
	[L,hits,error_rate] = te_func_handle(adaboost_model.parameters{turn},...
										 train_set,samples_weight,labels);
	if(error_rate==1)
		error_rate=1-eps;
	elseif(error_rate==0)
		error_rate=eps;
	end

	% The weight of the turn-th weak classifier
	adaboost_model.weights(turn) = log10((1-error_rate)/error_rate);
	C=likelihood2class(L);
	t_labeled=(C==labels);	% true labeled samples

	% Importance of the true classified samples is decreased for the next weak classifier
	samples_weight(t_labeled) = samples_weight(t_labeled)*...
					((error_rate)/(1-error_rate));				

	% Normalization
	samples_weight = samples_weight/sum(samples_weight);
end

% Normalization
adaboost_model.weights=adaboost_model.weights/sum(adaboost_model.weights);