Why is the predicted_label +1 even though it should be +1? Using LIBSVM

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sidra 2014-1-27

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https://ww2.mathworks.cn/matlabcentral/answers/113867-why-is-the-predicted_label-1-even-though-it-should-be-1-using-libsvm

评论： Walter Roberson 2014-1-27

I extracted the principal components of training and testing data. 'trainingdata.train' has feature values from both +1(face 1) and -1(all other faces) labels. 'testdata.train' has feature values from face 2 and no label since i want the SVM to predict its label. The "predicted_label" given by LIBSVM is +1 even though it should be -1.

[training_label_matrix, training_instance_matrix] = libsvmread('trainingdata.train');
[testing_label_matrix, testing_instance_matrix] = libsvmread('testdata.train');
model = svmtrain(training_label_matrix, training_instance_matrix);
[predicted_label] = svmpredict(testing_label_matrix, testing_instance_matrix, model);

Please point me out to what i am doing wrong.

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Walter Roberson 2014-1-27

svm is not going to do a good job on data that is not well separated or when not enough examples have been supplied to determine where the separation should be.

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