'Backward computation.
See Also
:meth:`BaseModule.backward`.
Parameters
out_grads : NDArray or list of NDArray, optional
Gradient on the outputs to be propagated back.
This parameter is only needed when bind is called
on outputs that are not a loss function.'

def backward(self, out_grads=None):

    assert (self.binded and self.params_initialized)
    self._exec_group.backward(out_grads=out_grads)
