class_docstr: Cumulative sum of array elements over a given axis.
code: def backward(self, indexes, grad_outputs):
      gy = grad_outputs[0]
      axis = self.axis
  
      if axis is not None:
          gx = flip.flip(cumsum(flip.flip(gy, axis), axis), axis)
      else:
          gx = flip.flip(cumsum(flip.flip(gy, 0), 0), 0)
          gx = gx.reshape(self._in_shape)
  
      return (gx,)
  
file_path: chainer/chainer/functions/math/cumsum.py
imports: import six
  from chainer import backend
  from chainer import function_node
  from chainer.functions.array import flip
  from chainer.utils import type_check
label_desc: Use image node_id 4 for calling the Cumsum obj's underlying member method code with example usage: obj.backward(indexes, grad_outputs) and returns: gx