def h(self, game: GameState):
if game.terminal():
return game.winner()
for _ in range(self.nbr_rollouts):
self.do_rollout(game)
return self.h_score(self.choose(game))
def _simulate(self, node: GameState):
"Returns the reward for a random simulation (to completion) of `node`"
invert_reward = True
while True:
if node.terminal():
reward = node.reward()
return 1 - reward if invert_reward else reward
node = node.push(node.random_move())
invert_reward = not invert_reward
def choose(self, node: GameState):
def score(n):
if self.N[n] == 0:
return float("-inf") # avoid unseen moves
return self.Q[n] / self.N[n] # average reward
"Choose the best successor of node. (Choose a move in the game)"
if node.terminal():
raise RuntimeError(f"choose called on terminal node {node}")
if node not in self.children:
return node.random_child()
return max(self.children[node], key=score)
