Set of hyperparameters.

def image_transformer2d_base():
  """Set of hyperparameters."""
  hparams = common_hparams.basic_params1()
  hparams.hidden_size = 512
  hparams.batch_size = 1
  hparams.max_length = 256
  hparams.dropout = 0.0
  hparams.clip_grad_norm = 0.  # i.e. no gradient clipping
  hparams.optimizer_adam_epsilon = 1e-9
  hparams.learning_rate_decay_scheme = "noam"
  hparams.learning_rate = 0.1
  hparams.learning_rate_warmup_steps = 4000
  hparams.initializer_gain = 0.2
  hparams.initializer = "uniform_unit_scaling"
  hparams.weight_decay = 0.0
  hparams.optimizer_adam_beta1 = 0.9
  hparams.optimizer_adam_beta2 = 0.98
  hparams.label_smoothing = 0.0
  hparams.bottom["targets"] = modalities.make_targets_bottom(
      modalities.image_channel_embeddings_bottom)
  hparams.top["targets"] = modalities.identity_top
  hparams.norm_type = "layer"
  hparams.layer_prepostprocess_dropout = 0.0
  hparams.add_hparam("filter_size", 512)  # Add new ones like this.

  # attention-related flags
  hparams.add_hparam("num_heads", 8)
  hparams.add_hparam("attention_key_channels", 0)
  hparams.add_hparam("attention_value_channels", 0)
  hparams.add_hparam("ffn_layer", "conv_hidden_relu")
  # All hyperparameters ending in "dropout" are automatically set to 0.0
  # when not in training mode.
  hparams.add_hparam("attention_dropout", 0.0)
  hparams.add_hparam("relu_dropout", 0.0)
  hparams.add_hparam("pos", "timing")  # timing, none
  hparams.add_hparam("nbr_decoder_problems", 1)
  hparams.add_hparam("num_output_layers", 3)
  hparams.add_hparam("block_size", 1)

  # image size related flags
  # assuming that the image has same height and width
  hparams.add_hparam("img_len", 32)
  hparams.add_hparam("num_channels", 3)
  # Local attention params
  hparams.add_hparam("local_and_global_att", False)
  hparams.add_hparam("block_length", 256)
  hparams.add_hparam("block_width", 128)
  # Local 2D attention params
  hparams.add_hparam("query_shape", (16, 16))
  hparams.add_hparam("memory_flange", (16, 32))
  hparams.add_hparam("num_encoder_layers", 4)
  hparams.add_hparam("num_decoder_layers", 8)
  # attention type related params
  hparams.add_hparam("enc_attention_type", cia.AttentionType.GLOBAL)
  hparams.add_hparam("dec_attention_type", cia.AttentionType.LOCAL_2D)
  hparams.add_hparam("block_raster_scan", False)

  # multipos attention params
  hparams.add_hparam("q_filter_width", 1)
  hparams.add_hparam("kv_filter_width", 1)

  hparams.add_hparam("unconditional", False)  # unconditional generation

  # relative embedding hparams
  hparams.add_hparam("shared_rel", False)
  return hparams