Author: Dan Homan
Date: 04:04:54 06/15/04
Go up one level in this thread
On June 15, 2004 at 05:28:26, Steve Maughan wrote:
>Dan,
>
>>When I shutoff the pruning from the swap function, I forgot to shut off the
>>swap function itself. When I do that, the results are the same, but the NPS
>>are a bit higher....
>
>What do you mean by swap function? Is this SEE pruning i.e. prune all losing
>captures? I'm already doing this and as you can see my qsearch is > 31%. Maybe
>I do have a problem.
>
>Thanks,
>
>Steve
The swap function just exchanges all possible material for that one square you
have moved to, and I think an SEE does all possible exchanges anywhere on the
board, but I am not sure. Regardless, I think they serve the same purpose, to
prune down the moves searched in the qsearch.
I prune more than losing captures; however, I also prune anything that doesn't
get me within a certain margin of alpha (futility pruning).
The margin is usually only 50 points (PAWN = 100), but I increase it if the
evaluation score for the current position is higher than the material score,
suggesting that there is lots of points to be gained from positional changes
resulting from captures. Here is the snippet of code...
best = pos.score_pos(alpha,beta); eval_count++;
if(best >= beta) {
pc[ply][ply].t = NOMOVE;
return best; // break if best > beta
}
// set futility cutoff 'delta_score' which is a global variable used
// in the generation of captures
if(best > alpha) alpha = best;
delta_score = alpha - MAX(best,pos.material) - 50;
delta_score = MAX(0,delta_score);
if(alpha > best) best = alpha;
I should also note that I do not count the first call to qsearch as a qsearch
node (that is just the leaf node from the main tree), but I do count all
subsequent calls to qsearch as qsearch nodes because those are leaves generated
by the qsearch. I think this is the same as your definition, but I wasn't 100%
sure.
- Dan
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