Thanks to visit codestin.com
Credit goes to github.com

Skip to content

Fix various issues in backgammon and expectiminimax #849

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 5 commits into from
Mar 15, 2018
Merged

Fix various issues in backgammon and expectiminimax #849

Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
855cc81
Fix expectiminimax and utility issues
AdityaDaflapurkar Mar 12, 2018
4add28f
Correct result function
AdityaDaflapurkar Mar 12, 2018
4151cbb
Fix issue with dice roll in different states
AdityaDaflapurkar Mar 15, 2018
ceda854
Refactor code
AdityaDaflapurkar Mar 15, 2018
9e52255
Merge with master
AdityaDaflapurkar Mar 15, 2018
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
38 changes: 22 additions & 16 deletions games.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -42,39 +42,40 @@ def min_value(state):
# ______________________________________________________________________________

def expectiminimax(state, game):
"""Returns the best move for a player after dice are thrown. The game tree
"""Return the best move for a player after dice are thrown. The game tree
includes chance nodes along with min and max nodes. [Figure 5.11]"""
player = game.to_move(state)

def max_value(state):
if game.terminal_test(state):
return game.utility(state, player)
def max_value(state, dice_roll):
v = -infinity
for a in game.actions(state):
v = max(v, chance_node(state, a))
game.dice_roll = dice_roll
return v

def min_value(state):
if game.terminal_test(state):
return game.utility(state, player)
def min_value(state, dice_roll):
v = infinity
for a in game.actions(state):
v = min(v, chance_node(state, a))
game.dice_roll = dice_roll
return v

def chance_node(state, action):
res_state = game.result(state, action)
if game.terminal_test(res_state):
return game.utility(res_state, player)
sum_chances = 0
num_chances = 21
dice_rolls = list(itertools.combinations_with_replacement([1, 2, 3, 4, 5, 6], 2))
if res_state.to_move == 'W':
for val in dice_rolls:
game.dice_roll = (-val[0], -val[1])
sum_chances += max_value(res_state) * (1/36 if val[0] == val[1] else 1/18)
sum_chances += max_value(res_state,
(-val[0], -val[1])) * (1/36 if val[0] == val[1] else 1/18)
elif res_state.to_move == 'B':
for val in dice_rolls:
game.dice_roll = val
sum_chances += min_value(res_state) * (1/36 if val[0] == val[1] else 1/18)
sum_chances += min_value(res_state, val) * (1/36 if val[0] == val[1] else 1/18)
return sum_chances / num_chances

# Body of expectiminimax:
Expand Down Expand Up @@ -403,6 +404,8 @@ def actions(self, state):
"""Returns a list of legal moves for a state."""
player = state.to_move
moves = state.moves
if len(moves) == 1 and len(moves[0]) == 1:
return moves
legal_moves = []
for move in moves:
board = copy.deepcopy(state.board)
Expand All @@ -414,10 +417,11 @@ def result(self, state, move):
board = copy.deepcopy(state.board)
player = state.to_move
board.move_checker(move[0], self.dice_roll[0], player)
board.move_checker(move[1], self.dice_roll[1], player)
if len(move) == 2:
board.move_checker(move[1], self.dice_roll[1], player)
to_move = ('W' if player == 'B' else 'B')
return GameState(to_move=to_move,
utility=self.compute_utility(board, move, to_move),
utility=self.compute_utility(board, move, player),
board=board,
moves=self.get_all_moves(board, to_move))

Expand All @@ -437,6 +441,8 @@ def get_all_moves(self, board, player):
all_points = board.points
taken_points = [index for index, point in enumerate(all_points)
if point[player] > 0]
if board.checkers_at_home(player) == 1:
return [(taken_points[0], )]
moves = list(itertools.permutations(taken_points, 2))
moves = moves + [(index, index) for index, point in enumerate(all_points)
if point[player] >= 2]
Expand All @@ -446,11 +452,11 @@ def display(self, state):
"""Display state of the game."""
board = state.board
player = state.to_move
print("Current State : ")
for index, point in enumerate(board.points):
if point['W'] != 0 or point['B'] != 0:
print("Point : ", index, " W : ", point['W'], " B : ", point['B'])
print("player : ", player)

print("Point : ", index, " W : ", point['W'], " B : ", point['B'])
print("To play : ", player)

def compute_utility(self, board, move, player):
"""If 'W' wins with this move, return 1; if 'B' wins return -1; else return 0."""
Expand Down Expand Up @@ -482,7 +488,7 @@ def __init__(self):
self.allow_bear_off = {'W': False, 'B': False}

def checkers_at_home(self, player):
"""Returns the no. of checkers at home for a player."""
"""Return the no. of checkers at home for a player."""
sum_range = range(0, 7) if player == 'W' else range(17, 24)
count = 0
for idx in sum_range:
Expand Down Expand Up @@ -516,7 +522,7 @@ def is_legal_move(self, start, steps, player):
return move1_legal and move2_legal

def move_checker(self, start, steps, player):
"""Moves a checker from starting point by a given number of steps"""
"""Move a checker from starting point by a given number of steps"""
dest = start + steps
dest_range = range(0, 24)
self.points[start][player] -= 1
Expand Down