code: def exponential_decay(step, rate, decay_steps, start_step=0):
      """A standard exponential decay, scaling the learning rate by :obj:`rate`
      every :obj:`decay_steps` steps.
      """
      return rate ** (
          max(step - start_step + decay_steps, 0) // decay_steps
      )
  
imports: import torch
  import torch.optim
  from torch.nn.utils import clip_grad_norm_
  import operator
  import functools
  from copy import copy
  from math import sqrt
  import types
  import os
  import importlib
  from onmt.utils.misc import fn_args
label_desc: Use image node_id 5 for calling a global function with example usage: exponential_decay(step, rate, decay_steps, start_step) and returns: unknown