Author: Robert Hyatt
Date: 06:14:57 09/17/99
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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... >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. >> >>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
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