class_docstr: Scheduler that decays by a fixed multiplicative rate at each valid step.
code: def train_step(self, scheduler_steps):
      pass
  
imports: import math
  from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.opt import Opt
  from abc import abstractmethod
  from torch import optim
  import numpy
  from parlai.core.exceptions import StopTrainException
  from parlai.utils.misc import warn_once
label_desc: Use image node_id 2 for calling the FixedLRScheduler obj's underlying member method code with example usage: obj.train_step(scheduler_steps) without return types