code: def forward(self):
      x = chainer.Variable(self.x)
      t = chainer.Variable(self.t)
      return functions.sigmoid_cross_entropy(x, t)
  
imports: import math
  import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer import utils
label_desc: Use image node_id 2 for calling the TestSigmoidCrossEntropyCudnnCall obj's underlying member method code with example usage: obj.forward() and returns: functions