!HELP: how to use svm_train function

[mm12344]

Does anyone know how to use the svm_train function?
I have followed the tutorial steps to use affine_train for image classification training, but the results were not very ideal. I want to change the training function into the svm_train. But the input of svm_train is different, I've got the following errors:
`Error using svmtrain (line 234)
Y must be a vector or a character array.

Error in svm_train (line 168)
model.svm = svmtrain(double(feature_class.'), ...

Error in demo3 (line 18)
model = svm_train(db1, train_set, svm_options);`
Y represents the features of all images which is 6814872 single array, but it seems that it can only be a vector, like maybe a 14872 array. I don't know how to fix it. Is there anyone can help?