class IterativePolicyEvaluation(object):
def __init__(self):
self.grid = GridWorld()
self.rewards = rewards
self.actions = actions
def initialize_V(self):
V = {}
S = []
for i in range(self.grid.rows):
for j in range(self.grid.cols):
V[(i, j)] = 0
if (i, j) not in [death, goal]:
S.append((i, j))
self.V = V
self.S = S
self.dynamic_p = 1.0 / len(S)
def value_step(self):
diff = 0
old_V = self.V
for s in self.S:
new_v = 0
old_v = old_V[s]
for a in self.actions:
self.grid.set_state(s)
self.grid.move(a)
s_new = self.grid.current_state()
r = self.rewards.get(s_new, 0)
if self.grid.game_over(s_new):
new_v += self.dynamic_p * r
break
else:
new_v += self.dynamic_p * (r + gamma * self.V[s_new])
self.V[s] = new_v
diff = max(diff, np.abs(old_v - new_v))
return diff
def policy_evaluation(self):
self.initialize_V()
while True:
diff = self.value_step()
if diff < delta:
self.print_values()
return None
def print_values(self):
for i in range(self.grid.rows):
print("------------------------")
for j in range(self.grid.cols):
v = self.V.get((i, j), 0)
if v >= 0:
print(" %.2f|" % v, end="")
else:
print("%.2f|" % v, end="")
print("")
print("------------------------")
class PolicyIteration(object):
def __init__(self):
self.grid = GridWorld()
self.rewards = rewards
self.actions = actions
def initialize_V(self):
V = {}
S = []
for i in range(self.grid.rows):
for j in range(self.grid.cols):
V[(i, j)] = 0
if (i, j) not in [death, goal]:
S.append((i, j))
self.V = V
self.S = S
self.dynamic_p = 1.0 / len(S)
def initialize_P(self):
P = {}
for i in range(self.grid.rows):
for j in range(self.grid.cols):
if (i, j) not in [death, goal]:
P[(i, j)] = np.random.choice(self.actions)
self.P = P
def value_step(self):
diff = 0
old_V = self.V
for s in self.S:
new_v = 0
old_v = old_V[s]
for a in self.actions:
self.grid.set_state(s)
self.grid.move(a)
s_new = self.grid.current_state()
r = self.rewards.get(s_new, 0)
new_v += self.dynamic_p * (r + gamma * self.V[s_new])
self.V[s] = new_v
diff = max(diff, np.abs(old_v - new_v))
return diff
def policy_evaluation(self):
while True:
diff = self.value_step()
if diff < delta:
return None
def improvement_step(self):
policy_stable = True
for s in self.S:
old_action = self.P[s]
action_values = []
for a in self.actions:
self.grid.set_state(s)
self.grid.move(a)
s_new = self.grid.current_state()
r = self.rewards.get(s_new, 0)
new_v = r + gamma * self.V[s_new]
action_values.append(new_v)
idx = np.argmax(action_values)
new_action = self.actions[idx]
self.P[s] = new_action
if old_action != new_action:
policy_stable = False
return policy_stable
def policy_iteration(self):
self.initialize_V()
self.initialize_P()
print("Initial Policy:")
self.print_policy()
while True:
self.policy_evaluation()
if self.improvement_step():
print("Final Policy:")
self.print_policy()
print("Final Values:")
self.print_values()
return None
def print_values(self):
for i in range(self.grid.rows):
print("------------------------")
for j in range(self.grid.cols):
v = self.V.get((i, j), 0)
if v >= 0:
print(" %.2f|" % v, end="")
else:
print("%.2f|" % v, end="")
print("")
print("------------------------")
def print_policy(self):
for i in range(self.grid.rows):
print("---------------------------")
for j in range(self.grid.cols):
a = self.P.get((i, j), '#')
print(" %s |" % a, end="")
print("")
print("------------------------")
from grid_world import GridWorld
gw = GridWorld(num_rows=4, num_columns=4)
gw.current_state = 14
print(gw.step('RIGHT'))