Author: Mats Forsén
Date: 13:20:52 04/08/98
Howdy folks,
I seem to be having a lot of troubles with my chess AI.. *sigh*..
I don't know if it is because my minimax function is shot to hell
so I'm asking you knowledgeable guys out there if there is anything
obvious wrong with it..
I'm also seeking some friendly soul to test my program and/or check
the code :) (It still sucks though) Win32 Console Text Interface.
One problem I have is with the path (show expected path).. Am I doing
it wrong? It sometimes (as below) sets a1a1 as a move, that is 0.
The position (WAC1) is:
2rr3k/pp3pp1/1nnqbN1p/3pN3/2pP4/2P3Q1/PPB4P/R4RK1 w - -
At a depth of 5 I get the following:
Time used: 21.239 s; Max depth: 5;
Nodes generated: 1007501; Nodes visited: 387775;
Ply: 0; Nodes Generated: 59; Nodes Visited: 1;
Ply: 1; Nodes Generated: 2202; Nodes Visited: 59;
Ply: 2; Nodes Generated: 6042; Nodes Visited: 106;
Ply: 3; Nodes Generated: 177503; Nodes Visited: 4437;
Ply: 4; Nodes Generated: 821695; Nodes Visited: 15291;
Ply: 5; Nodes Generated: 0; Nodes Visited: 367881;
Result: 200; Best path: g1h1 h6h5 e8d6 g7g6 a1a1
The computer suggests: 'g1h1'.
Here is my function:
int AI::negamax( Move * resulting_move, int playercolor, int depth, int
alpha,
int beta )
{
MoveList moves;
int result, curmove, cutoff = 0;
Move next_move;
nodes_visited[ depth ]++;
if( depth == 0 )
return board->Evaluate(playercolor);
board->GenerateMoves( playercolor, moves );
if( moves.num == 0 )
return board->Evaluate(playercolor); // No moves possible
nodes_generated[ depth ] += moves.num;
// sort_moves( moves );
curmove = moves.num;
while( curmove-- && !cutoff )
{
board->ApplyMove( moves.m[curmove] );
if( board->InCheck( playercolor ) )
{
board->UndoMove( moves.m[curmove] );
continue; // No check moves please
}
// Recurse using nega-max variant of alpha-beta
result = - negamax( &next_move, ( ~(playercolor & COLOR) & COLOR
),
depth-1, -beta, -alpha );
board->UndoMove( moves.m[curmove] );
if( result > alpha )
{
alpha = result;
*resulting_move = moves.m[curmove];
}
if( alpha > beta )
{
cutoff = 1;
historydata[ moves.m[curmove].where() ] += ( 1 << depth );
}
}
path.m[ depth ] = *resulting_move;
return result;
}
/ Mats Forsén
garnax@texoma.net
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