code: def rate(self, step):
      factor = self.model_size ** (-0.5) * min(
          step ** (-0.5), step * self.warmup ** (-1.5)
      )
      return self.learning_rate * factor
  
file_path: labml/helpers/labml_helpers/optimizer.py
imports: from typing import Tuple
  import torch
  from labml import tracker
  from labml.configs import BaseConfigs, option, meta_config
label_desc: Use image node_id 3 for calling the NoamOpt obj's underlying member method code with example usage: obj.rate(step) and returns: unknown