docstr: Add criterion-specific arguments to the parser.
docstr_tok: ["Add","criterion-specific","arguments","to","the","parser","."]
code: def add_args(parser):
      """Add criterion-specific arguments to the parser."""
      parser.add_argument(
          "--label-smoothing",
          default=0.0,
          type=float,
          metavar="D",
          help="[teacher decoder only] epsilon for label smoothing, 0 means "
          "no label smoothing.",
      )
      parser.add_argument(
          "--kd-weight",
          type=float,
          default=0.5,
          help=(
              "[student decoder only] mixture weight between the knowledge "
              "distillation and negative log likelihood losses. Must be in "
              "[0.0, 1.0].",
          ),
      )
  
file_path: translate/pytorch_translate/research/knowledge_distillation/dual_decoder_kd_loss.py
imports: import math
  from fairseq import utils
  from fairseq.criterions import LegacyFairseqCriterion, register_criterion
label_desc: Use image node_id 2 for calling the DualDecoderCriterion obj's underlying member method code with example usage: obj.add_args(parser) without return types