code: def _maxpool(x, ksize, stride=None):
      if stride is None:
          stride = ksize
  
      h = F.max_pooling_2d(x, ksize, stride=stride, pad=ksize - stride)
      if ksize > stride:
          h = h[:, :, ksize - stride :, ksize - stride :]
      return h
  
imports: from __future__ import division
  import itertools
  import numpy
  import chainer
  from chainer.backends import cuda
  import chainer.functions
  from chainer.links import Convolution2D
  from chainercv.links import Conv2DBNActiv
  from chainercv import utils
  from chainercv.links.model.yolo.yolo_base import YOLOBase
label_desc: Use image node_id 2 for calling a global function with example usage: _maxpool(x, ksize, stride) and returns: h