Old version - Adam.

def afx_adam():
  """Old version - Adam."""
  hparams = transformer.transformer_base_v2()
  hparams.optimizer_adam_beta1 = 0.9
  hparams.optimizer_adam_beta2 = 0.999
  hparams.symbol_modality_num_shards = 1
  hparams.batch_size = 2048
  hparams.optimizer = "adam"
  hparams.learning_rate_schedule = (
      "constant*rsqrt_decay*linear_warmup*rsqrt_hidden_size")
  hparams.learning_rate_constant = 2.0
  return hparams