def METHOD_NAME(self):
    # global_params is basically the global copy from the previously finished
    # synchronisation. param.data is local parameter after block_sync_freq
    # for the local gpu. so grad is difference between previously synced
    # model and currrent local model.
    for index, (param, global_param) in enumerate(
        zip(self.params, self.global_params)
    ):
        self.grads[index] = global_param - param.data