spinup/algos/pytorch/td3/td3.py [221:353]:
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    pi_optimizer = Adam(ac.pi.parameters(), lr=pi_lr)
    q_optimizer = Adam(q_params, lr=q_lr)

    # Set up model saving
    logger.setup_pytorch_saver(ac)

    def update(data, timer):
        # First run one gradient descent step for Q1 and Q2
        q_optimizer.zero_grad()
        loss_q, loss_info = compute_loss_q(data)
        loss_q.backward()
        q_optimizer.step()

        # Record things
        logger.store(LossQ=loss_q.item(), **loss_info)

        # Possibly update pi and target networks
        if timer % policy_delay == 0:

            # Freeze Q-networks so you don't waste computational effort 
            # computing gradients for them during the policy learning step.
            for p in q_params:
                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-networks so you can optimize it at next DDPG step.
            for p in q_params:
                p.requires_grad = True

            # Record things
            logger.store(LossPi=loss_pi.item())

            # 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 j in range(update_every):
                batch = replay_buffer.sample_batch(batch_size)
                update(data=batch, timer=j)

        # 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('Q1Vals', with_min_and_max=True)
            logger.log_tabular('Q2Vals', 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')
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spinup/exercises/pytorch/problem_set_1/exercise1_3.py [262:394]:
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    pi_optimizer = Adam(ac.pi.parameters(), lr=pi_lr)
    q_optimizer = Adam(q_params, lr=q_lr)

    # Set up model saving
    logger.setup_pytorch_saver(ac)

    def update(data, timer):
        # First run one gradient descent step for Q1 and Q2
        q_optimizer.zero_grad()
        loss_q, loss_info = compute_loss_q(data)
        loss_q.backward()
        q_optimizer.step()

        # Record things
        logger.store(LossQ=loss_q.item(), **loss_info)

        # Possibly update pi and target networks
        if timer % policy_delay == 0:

            # Freeze Q-networks so you don't waste computational effort 
            # computing gradients for them during the policy learning step.
            for p in q_params:
                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-networks so you can optimize it at next DDPG step.
            for p in q_params:
                p.requires_grad = True

            # Record things
            logger.store(LossPi=loss_pi.item())

            # 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 j in range(update_every):
                batch = replay_buffer.sample_batch(batch_size)
                update(data=batch, timer=j)

        # 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('Q1Vals', with_min_and_max=True)
            logger.log_tabular('Q2Vals', 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')
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