class_docstr: Computes the gradient of the Dropout function.
class_docstr_tok: ["Computes","the","gradient","of","the","Dropout","function","."]
code: def backward(self, indexes, gy):
      return DropoutGrad(self.mask).apply(gy)
  
imports: import numpy
  import chainer
  from chainer.backends import cuda
  from chainer.backends import intel64
  from chainer import configuration
  from chainer import function_node
  from chainer.utils import argument
  from chainer.utils import type_check
label_desc: Use image node_id 4 for calling the DropoutGrad obj's underlying member method code with example usage: obj.backward(indexes, gy) and returns: DropoutGrad