code: def backward(self, inputs, grad_outputs):
      # TODO(crcrpar): Implement this.
      raise NotImplementedError(
          "Double backward is not implemented for"
          " decorrelated batch normalization."
      )
  
imports: import numpy
  from chainer import backend
  from chainer import function_node
  from chainer.utils import argument
  from chainer.utils import type_check
label_desc: Use image node_id 3 for calling the DecorrelatedBatchNormalizationGrad obj's underlying member method code with example usage: obj.backward(inputs, grad_outputs) without return types