Author: Robert Hyatt
Date: 15:50:14 08/10/04
Go up one level in this thread
On August 10, 2004 at 17:36:53, Uri Blass wrote: >On August 10, 2004 at 14:47:02, Robert Hyatt wrote: > >>On August 10, 2004 at 13:42:24, Eric Oldre wrote: >> >>>On August 10, 2004 at 12:52:28, Robert Hyatt wrote: >>> >>>>On August 10, 2004 at 10:59:29, Tord Romstad wrote: >>>> >>>>>On August 10, 2004 at 10:35:29, Anthony Cozzie wrote: >>>>> >>>>>>Plus, if you have only PST eval you should be getting 3-4M nps, so SEE probably >>>>>>slows you down a _lot_. >>>>> >>>>>Yet another proof of how bad my programming skills are. With PST eval and >>>>>nothing >>>>>else, I get about 800,000 nps (on a PIV 2.4 GHz). Adding SEE slowed me down to >>>>>around 750,000 nps. >>>>> >>>>>Tord >>>> >>>> >>>>SEE slowed me down by 10%. Move ordering improved to speed me up 10%. Washed >>>>out to no advantage, _until_ I added the stuff about tossing out captures that >>>>can't bring the score back to within the alpha/beta window. That made me about >>>>2x faster overall, which is a _big_ gain. Stuart isn't getting all the >>>>advantages of SEE yet, and, in fact, It isn't necessary to use SEE on _every_ >>>>capture. IE for PxQ there is no need to see if that is +9 or +8. Either is >>>>good enough and there MVV/LVA is faster. >>> >>> >>> >>>Robert, >>>I haven't done any extensive testing to see if SEE pruning would improve the >>>strength of my engine. but i was worried that pruning moves in qsearch based on >>>a weak see score would eliminate moves where there would be additional >>>discovered attacks. >>> >>>For now I settled on the following. Over time i'll be able to tune the 2 const >>>values of 75 and 200 to more appropriate levels. I'm guessing evenutally they >>>will be lowered, but for now i'm trying to be "safer". >>> >>> >>>//get the see value of the move >>>move_estval = movestack->estscore[movestack->orderedmove[imove]]; >>> >>>//get the captured piece >>>chesspiece captured_piece = MoveTaken(move); >>> >>>//find value of the captured piece >>>int captured_piece_val = evalterms.material_vals[captured_piece]; >>> >>>bool can_gain_mater = true; >>>//init_score is the static eval before moving >>>if(captured_piece&&((captured_piece_val+init_score+75)<alpha)){can_gain_mater=false;} >>>if(captured_piece&&((move_estval+init_score+200)<alpha)){can_gain_mater=false;} >>>if(can_gain_mater){should_do_move=true;} >>> >>>In your opinion, is there any truth to my concerns about not discovering attacks >>>because of a see score that couldn't reach alpha? >>> >>>Eric >> >> >>I consider SEE scores to be simply estimates, since they do not worry about >>pinned pieces and the like. But then the entire q-search is only an estimate >>since it doesn't consider anything but captures (in Crafty). There are enough >>errors in only looking at captures to make your hair stand on end. Compounding >>this with SEE pruning doesn't change much at all. >> >>Best test is to try it. IE don't prune losing captures, and run a big test set. >> Then prune them and run it again. You will probably get almost a ply deeper by >>pruning, and your scores should go up, not down as a result (at least when I >>tested this it did. I've been doing this since the late 70's, with reasonable >>results. Others such as Bruce (Ferret) Stanback (Zarkov) and so forth have had >>the same results). >> >>The right thing to do is shrink the q-search, where the errors are, and make >>your normal search bigger where there is none of this highly selective pruning >>(ie looking at nothing but captures is _really_ selective) and its associated >>errors. > >I think that the right thing to do is to be more selective in the last plies. > >It does not mean to do the qsearch smaller. >You can start with more selective search than normal search but less selective >search than your qsearch in the first plies by including checks and captures and >only later to consider only good captures(I include queen promotions in the word >capture). > >Uri I don't disagree. Cray Blitz did that. It had a normal full-width part of the search, then a "tactical phase" that included captures, checks and some moves with significant threats, then only captures/checks, and finally tapering off to only captures. I may try that again one day as I did play with it in early versions of Crafty but decided to "keep it simple" for a while...
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