"""TanhGaussianMLPPolicy."""
import numpy as np
from torch import nn
from garage.torch.distributions import TanhNormal
from garage.torch.modules import GaussianMLPTwoHeadedModule
from garage.torch.policies.stochastic_policy import StochasticPolicy
[docs]class TanhGaussianMLPPolicy(StochasticPolicy):
"""Multiheaded MLP whose outputs are fed into a TanhNormal distribution.
A policy that contains a MLP to make prediction based on a gaussian
distribution with a tanh transformation.
Args:
env_spec (garage.envs.env_spec.EnvSpec): Environment specification.
hidden_sizes (list[int]): Output dimension of dense layer(s) for
the MLP for mean. For example, (32, 32) means the MLP consists
of two hidden layers, each with 32 hidden units.
hidden_nonlinearity (callable): Activation function for intermediate
dense layer(s). It should return a torch.Tensor. Set it to
None to maintain a linear activation.
hidden_w_init (callable): Initializer function for the weight
of intermediate dense layer(s). The function should return a
torch.Tensor.
hidden_b_init (callable): Initializer function for the bias
of intermediate dense layer(s). The function should return a
torch.Tensor.
output_nonlinearity (callable): Activation function for output dense
layer. It should return a torch.Tensor. Set it to None to
maintain a linear activation.
output_w_init (callable): Initializer function for the weight
of output dense layer(s). The function should return a
torch.Tensor.
output_b_init (callable): Initializer function for the bias
of output dense layer(s). The function should return a
torch.Tensor.
init_std (float): Initial value for std.
(plain value - not log or exponentiated).
min_std (float): If not None, the std is at least the value of min_std,
to avoid numerical issues (plain value - not log or exponentiated).
max_std (float): If not None, the std is at most the value of max_std,
to avoid numerical issues (plain value - not log or exponentiated).
std_parameterization (str): How the std should be parametrized. There
are two options:
- exp: the logarithm of the std will be stored, and applied a
exponential transformation
- softplus: the std will be computed as log(1+exp(x))
layer_normalization (bool): Bool for using layer normalization or not.
"""
def __init__(self,
env_spec,
hidden_sizes=(32, 32),
hidden_nonlinearity=nn.ReLU,
hidden_w_init=nn.init.xavier_uniform_,
hidden_b_init=nn.init.zeros_,
output_nonlinearity=None,
output_w_init=nn.init.xavier_uniform_,
output_b_init=nn.init.zeros_,
init_std=1.0,
min_std=np.exp(-20.),
max_std=np.exp(2.),
std_parameterization='exp',
layer_normalization=False):
super().__init__(env_spec, name='TanhGaussianPolicy')
self._obs_dim = env_spec.observation_space.flat_dim
self._action_dim = env_spec.action_space.flat_dim
self._module = GaussianMLPTwoHeadedModule(
input_dim=self._obs_dim,
output_dim=self._action_dim,
hidden_sizes=hidden_sizes,
hidden_nonlinearity=hidden_nonlinearity,
hidden_w_init=hidden_w_init,
hidden_b_init=hidden_b_init,
output_nonlinearity=output_nonlinearity,
output_w_init=output_w_init,
output_b_init=output_b_init,
init_std=init_std,
min_std=min_std,
max_std=max_std,
std_parameterization=std_parameterization,
layer_normalization=layer_normalization,
normal_distribution_cls=TanhNormal)
[docs] def forward(self, observations):
"""Compute the action distributions from the observations.
Args:
observations (torch.Tensor): Batch of observations on default
torch device.
Returns:
torch.distributions.Distribution: Batch distribution of actions.
dict[str, torch.Tensor]: Additional agent_info, as torch Tensors
"""
dist = self._module(observations)
ret_mean = dist.mean.cpu()
ret_log_std = (dist.variance.sqrt()).log().cpu()
return dist, dict(mean=ret_mean, log_std=ret_log_std)