code: def train_one_batch(self, x, y):
      out = self.forward(x)
      loss = autograd.softmax_cross_entropy(out, y)
      self.optimizer(loss)
      return out, loss
  
file_path: singa/examples/rnn/imdb_model.py
imports: from singa import autograd
  from singa import layer
  from singa import model
label_desc: Use image node_id 3 for calling the IMDBModel obj's underlying member method code with example usage: obj.train_one_batch(x, y) and returns: out,  loss