code: def backward(self, input_indexes, grad_outputs):
      raise RuntimeError(
          "F.softmax_cross_entropy was called with "
          "'enable_double_backprop=False' argument, but double-backprop "
          "is actually being performed. Please specify "
          "'enable_double_backprop=True' explicitly."
      )
  
imports: import numpy
  import six
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import function_node
  from chainer.functions.activation import log_softmax
  from chainer.utils import type_check
  from chainer import variable
  import chainerx
label_desc: Use image node_id 4 for calling the _SoftmaxCrossEntropyGrad_NoDoubleBackprop obj's underlying member method code with example usage: obj.backward(input_indexes, grad_outputs) without return types