code: def backward(ctx, grad_output):
      (ewma,) = ctx.saved_tensors
      return grad_output / ewma, None
  
imports: import math
  import warnings
  import torch
  import pyro
  from pyro import poutine
  from pyro.contrib.oed.search import Search
  from pyro.contrib.util import lexpand
  from pyro.infer import SVI, EmpiricalMarginal, Importance
  from pyro.infer.autoguide.utils import mean_field_entropy
  from pyro.util import torch_isinf, torch_isnan
label_desc: Use image node_id 2 for calling the _EwmaLogFn obj's underlying member method code with example usage: obj.backward(ctx, grad_output) and returns: unknown,  None