title: AttributeError: 'CrossEntropyLoss' object has no attribute 'backward'
body: <p>i am trying to train a very basic CNN on CIFAR10 data set and getting the following error :
  AttributeError: 'CrossEntropyLoss' object has no attribute 'backward'</p>
  
  <pre><code>criterion =nn.CrossEntropyLoss
  optimizer=optim.SGD(net.parameters(),lr=0.001,momentum=0.9)
  
  for epoch in range(2):  # loop over the dataset multiple times
          running_loss = 0.0
          for i, data in enumerate(trainloader, 0):
              # get the inputs
              inputs, labels = data
               # wrap them in Variable
              inputs, labels = Variable(inputs), Variable(labels)
  
              # zero the parameter gradients
              optimizer.zero_grad()
              # forward + backward + optimize
              outputs = net(inputs)
              loss = criterion(outputs, labels)
              loss.backward()
              optimizer.step()
              # print statistics
              running_loss += loss.data[0]
              if i % 2000 == 1999:    # print every 2000 mini-batches
                  print('[%d, %5d] loss: %.3f' %
                        (epoch + 1, i + 1, running_loss / 2000))
                  running_loss = 0.0
  </code></pre>