code: def rescale_grad(self, scale=None, param_name=None):
          
          if scale is None or param_name is None:
              return
          param_idx = self._exec_group.param_names.index(param_name)
          grad_vals = self._exec_group.grad_arrays[param_idx]
          for grad in grad_vals:
              grad[:] *= scale
docs: Rescale the gradient of provided parameters by a certain scale