from tensorflow.python.framework import ops

        multi_cell = rnn_cell.MultiRNNCell(
            [cell() for _ in range(num_layers)])
        outputs, final_state = core_rnn.static_rnn(
            multi_cell, inputs, dtype=dtypes.float32)
        trainable_variables = ops.get_collection(
            ops.GraphKeys.TRAINABLE_VARIABLES)
        gradients = gradients_impl.gradients([outputs, final_state],
                                             trainable_variables)
