Author: Ricardo Gibert
Date: 06:59:55 09/17/99
Go up one level in this thread
On September 17, 1999 at 09:14:57, Robert Hyatt wrote: >On September 17, 1999 at 02:47:34, Ricardo Gibert wrote: > >>On September 16, 1999 at 23:59:25, Robert Hyatt wrote: >> >>>First, a little background. I have been doing 'outside passed pawn' scoring >>>for years now, because I got tired of seeing Crafty lose endings where it was >>>a pawn up, and it traded down to the point where it was a king and pawns vs >>>king and pawns ending, where the opponent had an outside passed pawn that made >>>it an easy win... >> >>I was interested in a similar topic (for both middlegame & endgame), which is >>why I posted the following several days ago: >> >>Are their any estimates of how many distinct pawn structures get examined by >>computer programs over the course of a 5 minute blitz game? >> >>I wanted to make some approximate calculations of how much space a hashtable of >>such pawn structures would take, but I got zero response. >> > >I saw your post, but didn't want to think about the number. :) But when >you think about it,you have 16 pawns that can be on almost any of 48 squares, >so the number is huge. Just not as huge as the entire chess tree... > That's the problem, the number is huge if you count all legal pawn structures, but I was hoping that the average number of pawn structures that are examined by a program over the course of a typical game would be a more practical number. This is the number I need for my calculations. > > > >>Evaluating pawn structures for the endgame is tricky: W: Pa3,b2,c2; B: Pa5,b6. >>1) Here White can Q a pawn. 2) Shift the a-pawn from a5 to b5 and now White >>cannot Q a pawn without sacing a pawn and allowing Black to also Q! This can be >>a problem with pawns on both sides of the board. Your pawn "majority" will let >>you down. 3) If Blacks pawns are each advanced one square (B: Pa4, b5), then if >>white tries to get a passed pawn, Black may Q ahead of White e.g 1 b3? (1 b4 is >>less bad) 1...b4! and Black will Q an a-pawn well ahead of White. I'm assuming >>of course, that other material on the board do not interfere. >> > >I handle those cases with no problems, as far as the 'candidate passed pawn' >detection goes. ie white pawns on a2/b2/c2, black pawns on b5,b6 gets handled >correctly and recognized as 'no viable candidate' although it is possible to >sac a pawn to get a passer. But then the 'pawn race' code is used to handle >that case anyway. A surpising number of masters do not realize this one (b5,b6). They just assume if you "worsen" Blacks pawn structure, that Queening a pawn would not be more difficult. > >>> >>>OK... that was fairly easy to code using bitmaps... and it has worked well. >>>But once you get past that hurdle, you begin to see endings where you trade >>>down to a pawn-up ending, but your opponent has a queen-side majority that >>>turns into an outside passer outside the search horizon, and the same issue >>>comes up again. >>> >>>I am working on addressing this now, and am looking for a discussion on what >>>might be the best way to do this. >>> >>>I have completed a fairly accurate 'candidate passed pawn' analyzer. It is >>>in the EvaluatePawns() code so that it is all hashable and won't cost a fortune. >>> >>>All it does is simply look at each pawn that has no enemy pawn in front of it, >>>and decides whether pushing that pawn can make a passer or not. Again, not >>>hard using bitmaps, and in studying the results, it looks reasonable. My intent >>>is to use this in the absense of any outside passed pawns for one side, to see >>>if it has any potential outside passed pawns on that side of the board. And >>>for the usual 3 vs 2 queen-side majorities, it works cleanly and accurately. >>> >>>But what about 4 vs 3? Where the passer ends up on the d-file, which might >>>not be far enough away to cause problems. Or what about 3 vs 3, where one >>>side has pawns on a-b-c, the other side has pawns on b-c-d, and both end up >>>with a passer although the abc passer will be more distant. >> >>Careful! It is very often possible to Q a pawn on almost any file and not just >>the d-file by sacing material. This is sometimes relevant. Analogously, this can >>also happen with 3 vs 2 and 2 vs 1. > >I'm really not trying to evaluate what can queen.. only that 'here is a >candidate passer that will give the opponent trouble by decoying him to the >off-side of the board to stop it while I gobble elsewhere...' IE the classic >outside passer taken to a more distant level.. > > > > >> >>> >>>I guess my question is, has anyone given any thought to this? Or is anybody >>>even dealing with pawn majorities at present? I tend to not actually call this >>>majority code any longer, because it is _really_ candidate passed pawn >>>evaluation instead... >>> >>>My intention is to recognize that if the kings are on g1/g8, and white has >>>the a-b-c pawns and black just has b-c pawns, that this is a nearly winning >>>position. I am going to do just like I do with outside passers, that is, have >>>their value go up as material goes down, as they don't mean much with queens and >>>pieces on the board... >>> >>>Any comments, suggestions, ideas, etc? >>> >>>Obviously necessary, yet I don't see any evidence that any program does much >>>with this excepting for deep blue... >>> >>>Bob
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.