code: def backward(self, indexes, gy):
      (y,) = self.get_retained_outputs()
      return (BACKWORDC * chainer.functions.exp(y**2) * gy[0],)
  
file_path: chainer/chainer/functions/math/erfinv.py
imports: import math
  import chainer
  from chainer.backends import cuda
  from chainer import function_node
  from chainer import utils
  from chainer.utils import type_check
label_desc: Use image node_id 5 for calling the ErfInv obj's underlying member method code with example usage: obj.backward(indexes, gy) and returns: unknown