code: def forward_gpu(self, inputs):
      n, x = inputs
      self.retain_inputs((0, 1))
      return (
          utils.force_array(
              cuda.cupyx.scipy.special.polygamma(n, x), dtype=x.dtype
          ),
      )
  
file_path: chainer/chainer/functions/math/polygamma.py
imports: from chainer.backends import cuda
  from chainer import function_node
  from chainer import utils
  from chainer.utils import type_check
label_desc: Use image node_id 4 for calling the PolyGamma obj's underlying member method code with example usage: obj.forward_gpu(inputs) and returns: utils