code: def forward_expected(self, inputs):
      x0, x1 = inputs
  
      loss = 0.0
      for i in numpy.ndindex(x0.shape):
          loss += (x0[i] - x1[i]) ** 2
      loss /= x0.size
      loss = utils.force_array(loss).astype(x0.dtype)
      return (loss,)
  
file_path: chainer/tests/chainer_tests/functions_tests/loss_tests/test_mean_squared_error.py
imports: import unittest
  import numpy
  import chainer
  from chainer import functions
  from chainer import testing
  from chainer import utils
  from chainer.utils import type_check
label_desc: Use image node_id 4 for calling the TestMeanSquaredError obj's underlying member method code with example usage: obj.forward_expected(inputs) and returns: loss