nikita_s:

        self.classifier = nn.Sequential(nn.BatchNorm1d(512), nn.Linear(512, 4))
        self.bb = nn.Sequential(nn.BatchNorm1d(512), nn.Linear(512, 4))



The 4 at the end in classifier makes it 4 classes. If you want, there is some discussion about classifiers in our book that might be worthwhile and accessible (they are reading it currently over at PyTorch Book Reading Group - W&B Community).
I don’t know what the bb wants.