Author: Vladimir Medvedev
Date: 05:08:20 07/12/02
How to handle position repetitions during search?
I use the following method:
(pseudo-code)
int CountSearchRepetitions[MAXSIZE];
int CountHistoryRepetitions[MAXSIZE];
int AlphaBeta(Position pos, int alpha, int beta)
{
if( current_ply > 0 && CountHistoryRepetitions[ pos.GetHash() % MAXSIZE ]>0
)
{
return min( 0, beta );
}
if( CountSearchRepetitions[ pos.GetHash() % MAXSIZE ] > 1 )
{
return min( 0, beta );
}
while( get_next_move() )
{
pos.MakeMove();
SearchRepetition[ pos.GetHash() % MAXSIZE ] ++;
int eval = - AlphaBeta( pos, -beta, -alpha );
SearchRepetition[ pos.GetHash() % MAXSIZE ] --;
pos.UnmakeMove();
........
}
}
Is this correct? Shouldn't I return 0 instead min(0, beta)?
Is it good to add repetitions in game history to repetitions on the current
branch?
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Last modified: Thu, 07 Jul 11 08:48:38 -0700
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