def update(self, num_training_steps, eval_exp_id):
        """Updates the matrix with the accuracy value for a given task pair.

        :param num_training_steps: The ID of the current training experience.
        :param eval_exp_id: The ID of the evaluation experience.
        """
        if (max(num_training_steps, eval_exp_id) + 1) > self.matrix.size(0):
            self.add_new_task(max(num_training_steps, eval_exp_id) + 1)

        acc = self._accuracy.result()
        self.matrix[num_training_steps, eval_exp_id] = acc

        self._accuracy.reset()
Updates the matrix with the accuracy value for a given task pair.

        :param num_training_steps: The ID of the current training experience.
        :param eval_exp_id: The ID of the evaluation experience.
        
avalanche/evaluation/metrics/acc_matrix.py