def add_param_group(self, param_group):
        r"""Add a param group to the :class:`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 :class:`Optimizer` as
        training progresses.
        Args:
            param_group (dict): Specifies what Tensors should be optimized along
            with group specific optimization options.
        """
        param_group['n_avg'] = 0
        param_group['step_counter'] = 0
        self.optimizer.add_param_group(param_group)
Add a param group to the :class:`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 :class:`Optimizer` as
        training progresses.
        Args:
            param_group (dict): Specifies what Tensors should be optimized along
            with group specific optimization options.
        
fastreid/solver/optim/swa.py