code: def backward(ctx, grad):
      return grad
  
file_path: pyro/pyro/distributions/relaxed_straight_through.py
imports: import torch
  from torch.distributions.utils import clamp_probs
  from pyro.distributions.torch import RelaxedBernoulli, RelaxedOneHotCategorical
  from pyro.distributions.util import copy_docs_from
label_desc: Use image node_id 2 for calling the QuantizeCategorical obj's underlying member method code with example usage: obj.backward(ctx, grad) and returns: grad