Author: Andrew Williams
Date: 13:01:08 12/29/03
Go up one level in this thread
On December 29, 2003 at 15:26:27, Geoff wrote:
>Hi
>
>I have attempted to implement futility pruning for the first time today in my
>program. I was expecting it to be fairly straightforward to get working as far
>as reducing the number of nodes searched.
>Unfortunately I hit a strange problem that when I enable my futility and
>extended futility pruning I generally see an increase in the number of nodes
>searched and the time to depth can be greatly increased !!
>This weird effect is due to my beta cutoffs being made lower, I would guess I am
>seeing a typical 90% beta cutoff on the first move being reduced to 80% once I
>switch on the futility pruning. I wasn't anticipating this and for the moment
>cannot see a reason why it should have this adverse effect on my beta cutoffs ?
>Has anyone come across this problem before, or any ideas what could be going on
>? I have included a code snippet at the end in case I am doing something stupid
>? I wish the search archive was working as there is probably tons of relevant
>info on this topic. Thanks for any advice/suggestions.
>
> Regards Geoff
>
>
>
>
>For info
>
>My pruning code has been put in the normal search routine after the makemove but
>just before the call to the recursive alphabeta search function
>
>Futility code currently looks like this
>
>/* if not in check before move was made and not close to Mate score and not a
>capture or a promo move and not a checking move */
>
>if ((depth == 1) &&
> !weAreInCheck && (alpha > -9900) && (alpha < 9900) &&
> (!(gen_dat[i].m.b.bits & CAPTURE_MOVE)) &&
> (!(gen_dat[i].m.b.bits & PROMOTE_MOVE)) &&
> !inCheck(sideToMove))
>{
> lazyEval = lazyEvaluate();
>
> if ((lazyEval + FUTILITY_PRUNE_THRESHOLD) < alpha) /* le+300 */
> {
> /* dont bother searching this move any deeper just ignore it */
> futilityCutNodes++;
> takeBack();
> /* try next moved at this depth */
> continue;
> }
>}
>
>/* recurse search function */
>value = -search(-beta, -alpha, (depth + extensions - 1), TRUE);
I make sure that I have a legal move available before pruning stuff. I also
don't use lazy eval.
Andrew
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