def next_experience(self):
        """
        Moves to the next experience.

        This will consolidate the class accuracies for the current experience.

        This method can also be safely called before even calling the `update`
        method for the first time. In that case, this call will be ignored.
        """
        if not self._updated_once:
            return

        for task_id, mean_class_acc in self._get_curr_task_acc().items():
            self._prev_exps_accuracies[task_id].append(mean_class_acc)
        self._class_accuracies.reset()

        Moves to the next experience.

        This will consolidate the class accuracies for the current experience.

        This method can also be safely called before even calling the `update`
        method for the first time. In that case, this call will be ignored.
        
avalanche/evaluation/metrics/amca.py