code: def forward(self, x):
      return npx.Custom(x, op_type="relu")
  
imports: from __future__ import print_function
  import mxnet
  from mxnet import gluon, np, npx
  from mxnet import autograd
  from mxnet.gluon import nn
  import numpy
  import cv2
label_desc: Use image node_id 3 for calling the Activation obj's underlying member method code with example usage: obj.forward(x) and returns: npx