Hello, Are you trying to attempt a classification problem ?? If so..
As I can understand , you are trying to train some 12273 elements , each of them are defined by their 425 features. You haven't mentioned in the question how many classes you want to classify them into .
You have just mentioned "correct outputs stored in these matrices (the first and second ones, respectively)". If you are trying to classify into 2 classes, your target should be og size 2 * 12273 instead of 1 * 12273 , each row corresponding to their respective classes.