code: def train_one_batch_dis(self, x, y):
      # Training the Discriminative Net
      out = self.forward_dis(x)
      loss = self.binary_cross_entropy(out, y)
      # Only update the Discriminative Net
      for p, g in autograd.backward(loss):
          if "dis_net" in p.name:
              self.optimizer.apply(p.name, p, g)
      self.optimizer(loss)
      return out, loss
  
file_path: singa/examples/gan/model/gan_mlp.py
imports: from singa import layer
  from singa import model
  from singa import autograd
label_desc: Use image node_id 6 for calling the GAN_MLP obj's underlying member method code with example usage: obj.train_one_batch_dis(x, y) and returns: out,  loss