Is SEE really worthwhile?

Posted: Mon Jun 16, 2008 9:22 pm    Post subject: Is SEE really worthwhile?
I recall a thread some time back where the relative merits of MVV/LVA and SEE move-scoring was debated without a definitive conclusion being reached. I tried both schemes, and MVV/LVA seemed to work better, though I know others have reached the opposite conclusion. The other place SEE is often used is in qsearch, when determining whether to skip searching a particular sequence of captures, presumably to help avoid qsearch explosions. However in these cases, it seems obvious you could end up missing a sacrifice leading ultimately to a won game (e.g. unstoppable pawn). This is because the end-position of the skipped capture sequence is not evaluated. When I add SEE into my qsearch I only get a small speed improvement, maybe 5-10%. If SEE was worth an extra ply of search at any reasonable time control, it would be a different matter, but as it doesn't seem to, I can't really see the practical benefit! Am I missing something important? Vince

I think it depends a lot on other aspects of the engine if sorting by SEE, or pruning bad captures in QS, gives an improvement. Like you remark, the latter is a theoretically unsound pruning, and its effect cannot be judged by looking at search times for given positions, but must be measured in games to ensure that the move quality doesn't suffer more than the search-time reduction helps.

MVV/LVA is not a very inferior method at all, and very effectively suppresses QS explosions. Its Achilles' heel, the HxL captures, can often be remedied satisfactorily by not using pure MVV/LVA, but postponing such captures always, or dependent on some partial (but faster to obtain) information than a full SEE, e.g. if the piece is completely undefended or not.

mambofish wrote:
I recall a thread some time back where the relative merits of MVV/LVA and SEE move-scoring was debated without a definitive conclusion being reached. I tried both schemes, and MVV/LVA seemed to work better, though I know others have reached the opposite conclusion.


Are you asking if sorting with see score is worth it or if using see to find out if a capture is good or not is worth it ?
Knowing that a 'bad' capture like QxP is indeed winning is priceless and this capture must be searched first.

Quote:

The other place SEE is often used is in qsearch, when determining whether to skip searching a particular sequence of captures, presumably to help avoid qsearch explosions. However in these cases, it seems obvious you could end up missing a sacrifice leading ultimately to a won game (e.g. unstoppable pawn). This is because the end-position of the skipped capture sequence is not evaluated.


There is no such thing as winning sacrifice in qsearch because you do not search quiet move so you can not refute anything in qsearch (and we can not make threats like pawn/knight fork, etc).

Quote:

When I add SEE into my qsearch I only get a small speed improvement, maybe 5-10%. If SEE was worth an extra ply of search at any reasonable time control, it would be a different matter, but as it doesn't seem to, I can't really see the practical benefit!


See() uses more cpu, does your node count is reduced by only 10% ?
I'll try to find real numbers, this number is very suspect.

HJ.

http://64.68.157.89/forum/viewtopic.php?t=21821