from copy import deepcopy
import numpy as np
import torch
from torch.optim import Adam
import gym
import time
import spinup.algos.pytorch.ddpg.core as core
from spinup.utils.logx import EpochLogger
class ReplayBuffer:
"""
A simple FIFO experience replay buffer for DDPG agents.
"""
def __init__(self, obs_dim, act_dim, size):
self.obs_buf = np.zeros(core.combined_shape(size, obs_dim), dtype=np.float32)
self.obs2_buf = np.zeros(core.combined_shape(size, obs_dim), dtype=np.float32)
self.act_buf = np.zeros(core.combined_shape(size, act_dim), dtype=np.float32)
self.rew_buf = np.zeros(size, dtype=np.float32)
self.done_buf = np.zeros(size, dtype=np.float32)
self.ptr, self.size, self.max_size = 0, 0, size
def store(self, obs, act, rew, next_obs, done):
self.obs_buf[self.ptr] = obs
self.obs2_buf[self.ptr] = next_obs
self.act_buf[self.ptr] = act
self.rew_buf[self.ptr] = rew
self.done_buf[self.ptr] = done
self.ptr = (self.ptr+1) % self.max_size
self.size = min(self.size+1, self.max_size)
def sample_batch(self, batch_size=32):
idxs = np.random.randint(0, self.size, size=batch_size)
batch = dict(obs=self.obs_buf[idxs],
obs2=self.obs2_buf[idxs],
act=self.act_buf[idxs],
rew=self.rew_buf[idxs],
done=self.done_buf[idxs])
return {k: torch.as_tensor(v, dtype=torch.float32) for k,v in batch.items()}
def ddpg(env_fn, actor_critic=core.MLPActorCritic, ac_kwargs=dict(), seed=0,
steps_per_epoch=4000, epochs=100, replay_size=int(1e6), gamma=0.99,
polyak=0.995, pi_lr=1e-3, q_lr=1e-3, batch_size=100, start_steps=10000,
update_after=1000, update_every=50, act_noise=0.1, num_test_episodes=10,
max_ep_len=1000, logger_kwargs=dict(), save_freq=1):
"""
Deep Deterministic Policy Gradient (DDPG)
Args:
env_fn : A function which creates a copy of the environment.
The environment must satisfy the OpenAI Gym API.
actor_critic: The constructor method for a PyTorch Module with an ``act``
method, a ``pi`` module, and a ``q`` module. The ``act`` method and
``pi`` module should accept batches of observations as inputs,
and ``q`` should accept a batch of observations and a batch of
actions as inputs. When called, these should return:
=========== ================ ======================================
Call Output Shape Description
=========== ================ ======================================
``act`` (batch, act_dim) | Numpy array of actions for each
| observation.
``pi`` (batch, act_dim) | Tensor containing actions from policy
| given observations.
``q`` (batch,) | Tensor containing the current estimate
| of Q* for the provided observations
| and actions. (Critical: make sure to
| flatten this!)
=========== ================ ======================================
ac_kwargs (dict): Any kwargs appropriate for the ActorCritic object
you provided to DDPG.
seed (int): Seed for random number generators.
steps_per_epoch (int): Number of steps of interaction (state-action pairs)
for the agent and the environment in each epoch.
epochs (int): Number of epochs to run and train agent.
replay_size (int): Maximum length of replay buffer.
gamma (float): Discount factor. (Always between 0 and 1.)
polyak (float): Interpolation factor in polyak averaging for target
networks. Target networks are updated towards main networks
according to:
.. math:: \\theta_{\\text{targ}} \\leftarrow
\\rho \\theta_{\\text{targ}} + (1-\\rho) \\theta
where :math:`\\rho` is polyak. (Always between 0 and 1, usually
close to 1.)
pi_lr (float): Learning rate for policy.
q_lr (float): Learning rate for Q-networks.
batch_size (int): Minibatch size for SGD.
start_steps (int): Number of steps for uniform-random action selection,
before running real policy. Helps exploration.
update_after (int): Number of env interactions to collect before
starting to do gradient descent updates. Ensures replay buffer
is full enough for useful updates.
update_every (int): Number of env interactions that should elapse
between gradient descent updates. Note: Regardless of how long
you wait between updates, the ratio of env steps to gradient steps
is locked to 1.
act_noise (float): Stddev for Gaussian exploration noise added to
policy at training time. (At test time, no noise is added.)
num_test_episodes (int): Number of episodes to test the deterministic
policy at the end of each epoch.
max_ep_len (int): Maximum length of trajectory / episode / rollout.
logger_kwargs (dict): Keyword args for EpochLogger.
save_freq (int): How often (in terms of gap between epochs) to save
the current policy and value function.
"""
logger = EpochLogger(**logger_kwargs)
logger.save_config(locals())
torch.manual_seed(seed)
np.random.seed(seed)
env, test_env = env_fn(), env_fn()
obs_dim = env.observation_space.shape
act_dim = env.action_space.shape[0]
# Action limit for clamping: critically, assumes all dimensions share the same bound!
act_limit = env.action_space.high[0]
# Create actor-critic module and target networks
ac = actor_critic(env.observation_space, env.action_space, **ac_kwargs)
ac_targ = deepcopy(ac)
# Freeze target networks with respect to optimizers (only update via polyak averaging)
for p in ac_targ.parameters():
p.requires_grad = False
# Experience buffer
replay_buffer = ReplayBuffer(obs_dim=obs_dim, act_dim=act_dim, size=replay_size)
# Count variables (protip: try to get a feel for how different size networks behave!)
var_counts = tuple(core.count_vars(module) for module in [ac.pi, ac.q])
logger.log('\nNumber of parameters: \t pi: %d, \t q: %d\n'%var_counts)
# Set up function for computing DDPG Q-loss
def compute_loss_q(data):
o, a, r, o2, d = data['obs'], data['act'], data['rew'], data['obs2'], data['done']
q = ac.q(o,a)
# Bellman backup for Q function
with torch.no_grad():
q_pi_targ = ac_targ.q(o2, ac_targ.pi(o2))
backup = r + gamma * (1 - d) * q_pi_targ
# MSE loss against Bellman backup
loss_q = ((q - backup)**2).mean()
# Useful info for logging
loss_info = dict(QVals=q.detach().numpy())
return loss_q, loss_info
# Set up function for computing DDPG pi loss
def compute_loss_pi(data):
o = data['obs']
q_pi = ac.q(o, ac.pi(o))
return -q_pi.mean()
# Set up optimizers for policy and q-function
pi_optimizer = Adam(ac.pi.parameters(), lr=pi_lr)
q_optimizer = Adam(ac.q.parameters(), lr=q_lr)
# Set up model saving
logger.setup_pytorch_saver(ac)
def update(data):
# First run one gradient descent step for Q.
q_optimizer.zero_grad()
loss_q, loss_info = compute_loss_q(data)
loss_q.backward()
q_optimizer.step()
# Freeze Q-network so you don't waste computational effort
# computing gradients for it during the policy learning step.
for p in ac.q.parameters():
p.requires_grad = False
# Next run one gradient descent step for pi.
pi_optimizer.zero_grad()
loss_pi = compute_loss_pi(data)
loss_pi.backward()
pi_optimizer.step()
# Unfreeze Q-network so you can optimize it at next DDPG step.
for p in ac.q.parameters():
p.requires_grad = True
# Record things
logger.store(LossQ=loss_q.item(), LossPi=loss_pi.item(), **loss_info)
# Finally, update target networks by polyak averaging.
with torch.no_grad():
for p, p_targ in zip(ac.parameters(), ac_targ.parameters()):
# NB: We use an in-place operations "mul_", "add_" to update target
# params, as opposed to "mul" and "add", which would make new tensors.
p_targ.data.mul_(polyak)
p_targ.data.add_((1 - polyak) * p.data)
def get_action(o, noise_scale):
a = ac.act(torch.as_tensor(o, dtype=torch.float32))
a += noise_scale * np.random.randn(act_dim)
return np.clip(a, -act_limit, act_limit)
def test_agent():
for j in range(num_test_episodes):
o, d, ep_ret, ep_len = test_env.reset(), False, 0, 0
while not(d or (ep_len == max_ep_len)):
# Take deterministic actions at test time (noise_scale=0)
o, r, d, _ = test_env.step(get_action(o, 0))
ep_ret += r
ep_len += 1
logger.store(TestEpRet=ep_ret, TestEpLen=ep_len)
# Prepare for interaction with environment
total_steps = steps_per_epoch * epochs
start_time = time.time()
o, ep_ret, ep_len = env.reset(), 0, 0
# Main loop: collect experience in env and update/log each epoch
for t in range(total_steps):
# Until start_steps have elapsed, randomly sample actions
# from a uniform distribution for better exploration. Afterwards,
# use the learned policy (with some noise, via act_noise).
if t > start_steps:
a = get_action(o, act_noise)
else:
a = env.action_space.sample()
# Step the env
o2, r, d, _ = env.step(a)
ep_ret += r
ep_len += 1
# Ignore the "done" signal if it comes from hitting the time
# horizon (that is, when it's an artificial terminal signal
# that isn't based on the agent's state)
d = False if ep_len==max_ep_len else d
# Store experience to replay buffer
replay_buffer.store(o, a, r, o2, d)
# Super critical, easy to overlook step: make sure to update
# most recent observation!
o = o2
# End of trajectory handling
if d or (ep_len == max_ep_len):
logger.store(EpRet=ep_ret, EpLen=ep_len)
o, ep_ret, ep_len = env.reset(), 0, 0
# Update handling
if t >= update_after and t % update_every == 0:
for _ in range(update_every):
batch = replay_buffer.sample_batch(batch_size)
update(data=batch)
# End of epoch handling
if (t+1) % steps_per_epoch == 0:
epoch = (t+1) // steps_per_epoch
# Save model
if (epoch % save_freq == 0) or (epoch == epochs):
logger.save_state({'env': env}, None)
# Test the performance of the deterministic version of the agent.
test_agent()
# Log info about epoch
logger.log_tabular('Epoch', epoch)
logger.log_tabular('EpRet', with_min_and_max=True)
logger.log_tabular('TestEpRet', with_min_and_max=True)
logger.log_tabular('EpLen', average_only=True)
logger.log_tabular('TestEpLen', average_only=True)
logger.log_tabular('TotalEnvInteracts', t)
logger.log_tabular('QVals', with_min_and_max=True)
logger.log_tabular('LossPi', average_only=True)
logger.log_tabular('LossQ', average_only=True)
logger.log_tabular('Time', time.time()-start_time)
logger.dump_tabular()
if __name__ == '__main__':
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--env', type=str, default='HalfCheetah-v2')
parser.add_argument('--hid', type=int, default=256)
parser.add_argument('--l', type=int, default=2)
parser.add_argument('--gamma', type=float, default=0.99)
parser.add_argument('--seed', '-s', type=int, default=0)
parser.add_argument('--epochs', type=int, default=50)
parser.add_argument('--exp_name', type=str, default='ddpg')
args = parser.parse_args()
from spinup.utils.run_utils import setup_logger_kwargs
logger_kwargs = setup_logger_kwargs(args.exp_name, args.seed)
ddpg(lambda : gym.make(args.env), actor_critic=core.MLPActorCritic,
ac_kwargs=dict(hidden_sizes=[args.hid]*args.l),
gamma=args.gamma, seed=args.seed, epochs=args.epochs,
logger_kwargs=logger_kwargs)