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yeschess
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engine: engine now correctly uses the negamax algorithm

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NegaMax is a simplified version of the MiniMax algorithm that
doesn't need different subroutines for the different colors.
The testcases were selected and extended.
Evaluation now has values for draws and wins.
master
TiynGER 4 years ago
parent 9ea20b6c1f
commit 9095cf8eee
3 changed files with 75 additions and 48 deletions
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2
README.md
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@ -38,4 +38,4 @@ Due to easier off the board checking a
### Engine
The engine uses a simple implementation of the
[Minimax](https://www.chessprogramming.org/Minimax)-algorithm.
[NegaMax](https://www.chessprogramming.org/NegaMax)-algorithm.

64
src/engine.nim
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@ -13,10 +13,9 @@ const
BishopVal = 3 ## `BishopVal` is the engines value for a bishop.
RookVal = 5 ## `RookVal` is the engines value for a rook.
QueenVal = 9 ## `QueenVal` is the engines value for a queen.
CheckmateVal = 1000 ## `CheckmateVal` is the engines value for a checkmate.
CheckmateVal = -1000 ## `CheckmateVal` is the engines value for a checkmate.
DrawVal = 0 ## `DrawVal` is the engines value for a draw.
HiVal = 1000000 ## `HiVal` is the highest possible value (used in minimax).
LoVal = -HiVal ## `LoVal` is the lowest possible value (used in minimax).
LoVal = -1000000 ## `LoVal` is a value always lower than any evaluation.
proc pieceEval*(game: Game): int =
## Returns the evaluation of existing pieces on the `board`
@ -50,14 +49,25 @@ proc pieceEval*(game: Game): int =
proc evaluate(game: Game): int =
## Returns a complete evaluation of a `game` with player `toMove` about to make
## a move.
var evaluation = game.pieceEval()
var evaluation: int
if game.isCheckmate(game.toMove):
evaluation = ord(game.toMove) * CheckmateVal
if game.isStalemate(game.toMove):
evaluation = DrawVal
else:
evaluation = game.pieceEval()
if game.isDrawClaimable():
if game.toMove == Color.White:
evaluation = max(DrawVal, evaluation)
else:
evaluation = min(DrawVal, evaluation)
return evaluation
proc spanMoveTree*(game: Game, depth: int): MoveTree =
## Create and return a Movetree of a given `game` with a given maximum `depth`.
var mTree: MoveTree
mTree.game = game
if depth != 1 and not game.isCheckmate(game.toMove) and not game.isStalemate(game.toMove):
if depth != 0 and not game.isCheckmate(game.toMove) and not game.isStalemate(game.toMove):
let possibleMoves = game.genLegalMoves(game.toMove)
for move in possibleMoves:
var tmpGame = game
@ -65,46 +75,30 @@ proc spanMoveTree*(game: Game, depth: int): MoveTree =
mTree.children.add(spanMoveTree(tmpGame, depth-1))
return mTree
proc minimax*(mTree: MoveTree): int =
proc negaMax*(mTree: MoveTree): int =
## Return the value of the root node of a given `MoveTree`
if mTree.children == []:
return evaluate(mTree.game)
var bestVal: int
var tmpVal: int
if mTree.game.toMove == Color.White:
bestVal = LoVal
for child in mTree.children:
tmpVal = minimax(child)
bestVal = max(bestVal, tmpVal)
else:
bestVal = HiVal
for child in mTree.children:
tmpVal = minimax(child)
bestVal = min(bestVal, tmpVal)
return mTree.game.evaluate()
var bestVal = LoVal
for child in mTree.children:
var tmpVal = -negaMax(child)
bestVal = max(bestVal, tmpVal)
return bestVal
proc bestMove*(game: Game, depth: int): Move =
## Generate a MoveTree of a `game` with a given `depth`, run Minimax and return
## Generate a MoveTree of a `game` with a given `depth`, run negaMax and return
## the best evaluated move.
var moves = game.genLegalMoves(game.toMove)
var bestMove: Move
var bestEval: int
if game.toMove == Color.White:
bestEval = LoVal
else:
bestEval = HiVal
bestEval = LoVal
for move in moves:
var tmpGame = game
tmpGame.checkedMove(move)
var tmpEval = tmpGame.evaluate()
if game.toMove == Color.White:
if tmpEval > bestEval:
bestEval = tmpEval
bestMove = move
else:
if tmpEval < bestEval:
bestEval = tmpEval
bestMove = move
var tmpMTree = tmpGame.spanMoveTree(depth)
var tmpEval = -tmpMTree.negaMax()
echo("move:", moveToNotation(move),"; eval:", tmpEval)
if tmpEval > bestEval:
bestEval = tmpEval
bestMove = move
return bestMove

57
src/engineTest.nim
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@ -1,5 +1,4 @@
import einheit
import algorithm
import ./chess
import ./engine
@ -12,7 +11,7 @@ testSuite GameTest of TestSuite:
method setup() =
self.game = initGame()
method testPieceEval() =
method testPieceEvalStalemate() =
self.game = initGame([
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, WKing, 0, 0, 0, 0,
@ -37,10 +36,10 @@ testSuite GameTest of TestSuite:
0, 0, 0, 0, 0, BKing, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0
], Color.Black)
var mTree = self.game.spanMoveTree(2)
var mTree = self.game.spanMoveTree(1)
self.check(mTree.children == [])
method testManualMiniMaxEval() =
method testBestMoveProm() =
self.game = initGame([
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, WKing, 0, 0, 0, 0,
@ -48,15 +47,18 @@ testSuite GameTest of TestSuite:
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, WPawn, BKing, 0, 0,
0, 0, 0, WPawn, 0, BKing, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0
], Color.Black)
var mTree = self.game.spanMoveTree(2)
var evaluation = mTree.minimax()
self.check(evaluation == 0)
], Color.White)
var testBestMove = self.game.bestMove(2)
self.check(testBestMove.start != 0)
self.check(indToField(testBestMove.start) == "e7")
self.check(indToField(testBestMove.dest) == "e8")
method testBestMove() =
var testGame = initGame([
method testBestMoveStopProm() =
self.game = initGame([
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, WKing, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
@ -66,10 +68,41 @@ testSuite GameTest of TestSuite:
0, 0, 0, 0, WPawn, BKing, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0
], Color.Black)
var testBestMove = testGame.bestMove(2)
var testBestMove = self.game.bestMove(2)
self.check(testBestMove.start != 0)
self.check(indToField(testBestMove.start) == "c7")
self.check(indToField(testBestMove.dest) == "d7")
method testBestMoveTacticBlack() =
self.game = initGame([
0, 0, 0, 0, 0, 0, 0, 0,
0, WRook, 0, WKing, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, WPawn, 0, 0, 0, 0, 0,
0, BPawn, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, BRook, 0, 0, 0, BKing, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0
], Color.Black)
var testBestMove = self.game.bestMove(2)
self.check(testBestMove.start != 0)
self.check(indToField(testBestMove.start) != "g5" or indToField(testBestMove.dest) != "f4")
method testBestMoveTacticWhite() =
self.game = initGame([
0, 0, 0, 0, 0, 0, 0, 0,
0, WRook, 0, WKing, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, WPawn, 0, 0, 0, 0, 0, 0,
0, 0, BPawn, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, BRook, 0, 0, 0, BKing, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0
], Color.White)
var testBestMove = self.game.bestMove(2)
self.check(testBestMove.start != 0)
self.check(indToField(testBestMove.start) != "g4" or indToField(testBestMove.dest) != "f5")
when isMainModule:
einheit.runTests()

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