TPU related imagenet model.

def imagetransformer_b12l_4h_b128_h512_uncond_dr01_im():
  """TPU related imagenet model."""
  hparams = imagetransformer_b12l_4h_b256_uncond_dr03_tpu()
  update_hparams_for_tpu(hparams)
  hparams.batch_size = 4
  hparams.optimizer = "Adafactor"
  hparams.learning_rate_schedule = "rsqrt_decay"
  hparams.learning_rate_warmup_steps = 6000
  hparams.layer_prepostprocess_dropout = 0.1
  return hparams