code: def noam_decay(step, warmup_steps, model_size):
      """Learning rate schedule described in
      https://arxiv.org/pdf/1706.03762.pdf.
      """
      return model_size ** (-0.5) * min(
          step ** (-0.5), step * warmup_steps ** (-1.5)
      )
  
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 3 for calling a global function with example usage: noam_decay(step, warmup_steps, model_size) and returns: unknown