docstr: Multiplies grads by a constant ``c``.
docstr_tok: ["Multiplies","grads","by","a","constant","``","c","``","."]
code: def multiply_grads(self, c):
      """Multiplies grads by a constant ``c``."""
      if self._needs_sync:
          self._sync_fp16_grads_to_fp32(c)
      else:
          self.fp32_params.grad.data.mul_(c)
  
imports: from itertools import chain
  import torch
  from fairseq import utils
  from fairseq.optim.fp16_optimizer import DynamicLossScaler
label_desc: Use image node_id 7 for calling the Fairseq_FP16OptimizerMixin obj's underlying member method code with example usage: obj.multiply_grads(c) without return types