code: def backward(self, inputs_val, logits_grad_val):
      inputs_grad_val = self.session.run(
          self.bw_gradients,
          feed_dict={
              self.inputs: inputs_val,
              self.bw_gradient_pre: logits_grad_val,
          },
      )
      return inputs_grad_val
  
file_path: advertorch/advertorch_examples/attack_madry_et_al_models/madry_et_al_utils.py
imports: import os
  import sys
  from pathlib import Path
  import tensorflow
  import torch
  from advertorch.bpda import BPDAWrapper
  from advertorch_examples.utils import ROOT_PATH, mkdir
label_desc: Use image node_id 2 for calling the WrappedTfModel obj's underlying member method code with example usage: obj.backward(inputs_val, logits_grad_val) and returns: inputs_grad_val