code: def __call__(self, x):
      return chainer.functions.sum(self.a(x))
  
file_path: espnet/test/test_optimizer.py
imports: import chainer
  import numpy
  import pytest
  import torch
  from espnet.optimizer.factory import dynamic_import_optimizer
  from espnet.optimizer.pytorch import OPTIMIZER_FACTORY_DICT
label_desc: Use image node_id 2 for calling the ChModel obj's underlying member method code with example usage: obj.__call__(x) and returns: chainer