whenever i use F.nll_loss, everything is fine it works very vell, but during test set it outputs the same class, it predicts 1 (dogs =1 cats=0) all time.at firs all images are 50x50x3 then iconvert them to 50x50x1, target values at firs are vectors [1,0] =dog [0,1]=cat. then i convert them to single number.also int network i am using softmax function