matlab libsvm: unable to predict

Question

I am using libsvm on Matlab. I want to build a model and use this model for prediction. It is wired that the returns of svmpredict ([predict_label, accuracy_all, prob_values]) are empty. Here is my simple code:

svm_model = svmtrain([train_label],[train],'-t 2, -c 100 -q');
[predict_label, accuracy_all, prob_values] = svmpredict(testlabels,testdata,svm_model,'-q, -b 1');

[predict_label, accuracy_all, prob_values] are 0x0 matrix. And also Matlab also shows some warning information:

Usage: [predicted_label, accuracy, decision_values/prob_estimates] = svmpredict(testing_label_vector, testing_instance_matrix, model, 'libsvm_options')
Parameters:
  model: SVM model structure from svmtrain.
  libsvm_options:
    -b probability_estimates: whether to predict probability estimates, 0 or 1 (default 0); one-class SVM not supported yet
Returns:
  predicted_label: SVM prediction output vector.
  accuracy: a vector with accuracy, mean squared error, squared correlation coefficient.
  prob_estimates: If selected, probability estimate vector.

Can anyone help me?

Answer 1

What is q in the SVM model ? where is it's value ?

there is two parameters in the SVM which need to be well defined c and g , you have put 100 as value of c but ther is no value for q (or must be g which is called gamma)

this what you need

 cmd = ['-t 2 -c ',num2str(C), ' -g ',num2str(gamma) ];
model = svmtrain2(trainClass, trainData, cmd);
[predClass, acc, decVals] = svmpredict(testClass, testData, model);

Also i think that svmtrain must be renamed svmtrain2 to avoid the confusion with svmtrain function of matlab.