fcnet.py

import numpy as np
import gymnasium as gym
from typing import Dict

from ray.rllib.models.tf.misc import normc_initializer
from ray.rllib.models.tf.tf_modelv2 import TFModelV2
from ray.rllib.models.utils import get_activation_fn
from ray.rllib.utils.annotations import OldAPIStack
from ray.rllib.utils.framework import try_import_tf
from ray.rllib.utils.typing import TensorType, List, ModelConfigDict

tf1, tf, tfv = try_import_tf()


@OldAPIStack
class FullyConnectedNetwork(TFModelV2):
    """Generic fully connected network implemented in ModelV2 API."""

    def __init__(
        self,
        obs_space: gym.spaces.Space,
        action_space: gym.spaces.Space,
        num_outputs: int,
        model_config: ModelConfigDict,
        name: str,
    ):
        super(FullyConnectedNetwork, self).__init__(
            obs_space, action_space, num_outputs, model_config, name
        )

        hiddens = list(model_config.get("fcnet_hiddens", [])) + list(
            model_config.get("post_fcnet_hiddens", [])
        )
        activation = model_config.get("fcnet_activation")
        if not model_config.get("fcnet_hiddens", []):
            activation = model_config.get("post_fcnet_activation")
        activation = get_activation_fn(activation)
        no_final_linear = model_config.get("no_final_linear")
        vf_share_layers = model_config.get("vf_share_layers")
        free_log_std = model_config.get("free_log_std")

        # Generate free-floating bias variables for the second half of
        # the outputs.
        if free_log_std:
            assert num_outputs % 2 == 0, (
                "num_outputs must be divisible by two",
                num_outputs,
            )
            num_outputs = num_outputs // 2
            self.log_std_var = tf.Variable(
                [0.0] * num_outputs, dtype=tf.float32, name="log_std"
            )

        # We are using obs_flat, so take the flattened shape as input.
        inputs = tf.keras.layers.Input(
            shape=(int(np.product(obs_space.shape)),), name="observations"
        )
        # Last hidden layer output (before logits outputs).
        last_layer = inputs
        # The action distribution outputs.
        logits_out = None
        i = 1

        # Create layers 0 to second-last.
        for size in hiddens[:-1]:
            last_layer = tf.keras.layers.Dense(
                size,
                name="fc_{}".format(i),
                activation=activation,
                kernel_initializer=normc_initializer(1.0),
            )(last_layer)
            i += 1

        # The last layer is adjusted to be of size num_outputs, but it's a
        # layer with activation.
        if no_final_linear and num_outputs:
            logits_out = tf.keras.layers.Dense(
                num_outputs,
                name="fc_out",
                activation=activation,
                kernel_initializer=normc_initializer(1.0),
            )(last_layer)
        # Finish the layers with the provided sizes (`hiddens`), plus -
        # iff num_outputs > 0 - a last linear layer of size num_outputs.
        else:
            if len(hiddens) > 0:
                last_layer = tf.keras.layers.Dense(
                    hiddens[-1],
                    name="fc_{}".format(i),
                    activation=activation,
                    kernel_initializer=normc_initializer(1.0),
                )(last_layer)
            if num_outputs:
                logits_out = tf.keras.layers.Dense(
                    num_outputs,
                    name="fc_out",
                    activation=None,
                    kernel_initializer=normc_initializer(0.01),
                )(last_layer)
            # Adjust num_outputs to be the number of nodes in the last layer.
            else:
                self.num_outputs = ([int(np.product(obs_space.shape))] + hiddens[-1:])[
                    -1
                ]

        # Concat the log std vars to the end of the state-dependent means.
        if free_log_std and logits_out is not None:

            def tiled_log_std(x):
                return tf.tile(tf.expand_dims(self.log_std_var, 0), [tf.shape(x)[0], 1])

            log_std_out = tf.keras.layers.Lambda(tiled_log_std)(inputs)
            logits_out = tf.keras.layers.Concatenate(axis=1)([logits_out, log_std_out])

        last_vf_layer = None
        if not vf_share_layers:
            # Build a parallel set of hidden layers for the value net.
            last_vf_layer = inputs
            i = 1
            for size in hiddens:
                last_vf_layer = tf.keras.layers.Dense(
                    size,
                    name="fc_value_{}".format(i),
                    activation=activation,
                    kernel_initializer=normc_initializer(1.0),
                )(last_vf_layer)
                i += 1

        value_out = tf.keras.layers.Dense(
            1,
            name="value_out",
            activation=None,
            kernel_initializer=normc_initializer(0.01),
        )(last_vf_layer if last_vf_layer is not None else last_layer)

        self.base_model = tf.keras.Model(
            inputs, [(logits_out if logits_out is not None else last_layer), value_out]
        )

    def forward(
        self,
        input_dict: Dict[str, TensorType],
        state: List[TensorType],
        seq_lens: TensorType,
    ) -> (TensorType, List[TensorType]):
        model_out, self._value_out = self.base_model(input_dict["obs_flat"])
        return model_out, state

    def value_function(self) -> TensorType:
        return tf.reshape(self._value_out, [-1])