add_param_group(param_group)
  Add a param group to the "Optimizer" s *param_groups*.

  This can be useful when fine tuning a pre-trained network as
  frozen layers can be made trainable and added to the "Optimizer"
  as training progresses.

  Parameters:
     **param_group** (*dict*) -- Specifies what Tensors should be
     optimized along with group specific optimization options.

load_state_dict(state_dict)
  Loads the optimizer state.

  Parameters:
     **state_dict** (*dict*) -- optimizer state. Should be an
     object returned from a call to "state_dict()".

register_step_post_hook(hook)
  Register an optimizer step post hook which will be called after
  optimizer step. It should have the following signature:

     hook(optimizer, args, kwargs) -> None

  The "optimizer" argument is the optimizer instance being used.

  Parameters:
     **hook** (*Callable*) -- The user defined hook to be
     registered.
