import torch
[docs]def compute_advantage_montecarlo(V, s, ss, r, absorbing, gamma):
"""
Function to estimate the advantage and new value function target
over a dataset. The value function is estimated using rollouts
(monte carlo estimation).
Args:
V (Regressor): the current value function regressor;
s (torch.tensor): the set of states in which we want
to evaluate the advantage;
ss (torch.tensor): the set of next states in which we want
to evaluate the advantage;
r (torch.tensor): the reward obtained in each transition
from state s to state ss;
absorbing (torch.tensor): an array of boolean flags indicating
if the reached state is absorbing;
gamma (float): the discount factor of the considered problem.
Returns:
The new estimate for the value function of the next state
and the advantage function.
"""
with torch.no_grad():
r = r.squeeze()
q = torch.zeros(len(r))
v = V(s).squeeze()
q_next = V(ss[-1]).squeeze().item()
for rev_k in range(len(r)):
k = len(r) - rev_k - 1
q_next = r[k] + gamma * q_next * (1 - absorbing[k].int())
q[k] = q_next
adv = q - v
return q[:, None], adv[:, None]
[docs]def compute_advantage(V, s, ss, r, absorbing, gamma):
"""
Function to estimate the advantage and new value function target
over a dataset. The value function is estimated using bootstrapping.
Args:
V (Regressor): the current value function regressor;
s (torch.tensor): the set of states in which we want
to evaluate the advantage;
ss (torch.tensor): the set of next states in which we want
to evaluate the advantage;
r (torch.tensor): the reward obtained in each transition
from state s to state ss;
absorbing (torch.tensor): an array of boolean flags indicating
if the reached state is absorbing;
gamma (float): the discount factor of the considered problem.
Returns:
The new estimate for the value function of the next state
and the advantage function.
"""
with torch.no_grad():
v = V(s).squeeze()
v_next = V(ss).squeeze() * (1 - absorbing.int())
q = r + gamma * v_next
adv = q - v
return q[:, None], adv[:, None]
[docs]def compute_gae(V, s, ss, r, absorbing, last, gamma, lam):
"""
Function to compute Generalized Advantage Estimation (GAE)
and new value function target over a dataset.
"High-Dimensional Continuous Control Using Generalized
Advantage Estimation".
Schulman J. et al.. 2016.
Args:
V (Regressor): the current value function regressor;
s (torch.tensor): the set of states in which we want
to evaluate the advantage;
ss (torch.tensor): the set of next states in which we want
to evaluate the advantage;
r (torch.tensor): the reward obtained in each transition
from state s to state ss;
absorbing (torch.tensor): an array of boolean flags indicating
if the reached state is absorbing;
last (torch.tensor): an array of boolean flags indicating
if the reached state is the last of the trajectory;
gamma (float): the discount factor of the considered problem;
lam (float): the value for the lamba coefficient used by GEA
algorithm.
Returns:
The new estimate for the value function of the next state
and the estimated generalized advantage.
"""
with torch.no_grad():
v = V(s)
v_next = V(ss)
gen_adv = torch.empty_like(v)
for rev_k in range(len(v)):
k = len(v) - rev_k - 1
if last[k] or rev_k == 0:
gen_adv[k] = r[k] - v[k]
if not absorbing[k]:
gen_adv[k] += gamma * v_next[k]
else:
gen_adv[k] = r[k] + gamma * v_next[k] - v[k] + gamma * lam * gen_adv[k + 1]
return gen_adv + v, gen_adv