def update(self):
        """Updates parameters according to the installed optimizer and the gradients computed
        in the previous forward-backward batch.

        When KVStore is used to update parameters for multi-device or multi-machine training,
        a copy of the parameters are stored in KVStore. Note that for `row_sparse` parameters,
        this function does update the copy of parameters in KVStore, but doesn't broadcast the
        updated parameters to all devices / machines. Please call `prepare` to broadcast
        `row_sparse` parameters with the next batch of data.

        See Also
        ----------
        :meth:`BaseModule.update`.
        """
        assert self.binded and self.params_initialized and self.optimizer_initialized

        self._params_dirty = True
        if self._update_on_kvstore:
            _update_params_on_kvstore(self._exec_group.param_arrays,
                                      self._exec_group.grad_arrays,
                                      self._kvstore, self._exec_group.param_names)
        else:
            _update_params(self._exec_group.param_arrays,
                           self._exec_group.grad_arrays,
                           updater=self._updater,
                           num_device=len(self._context),
                           kvstore=self._kvstore,
                           param_names=self._exec_group.param_names)
Updates parameters according to the installed optimizer and the gradients computed
        in the previous forward-backward batch.

        When KVStore is used to update parameters for multi-device or multi-machine training,
        a copy of the parameters are stored in KVStore. Note that for `row_sparse` parameters,
        this function does update the copy of parameters in KVStore, but doesn't broadcast the
        updated parameters to all devices / machines. Please call `prepare` to broadcast
        `row_sparse` parameters with the next batch of data.

        See Also
        ----------
        :meth:`BaseModule.update`.