Author: Robert Hyatt
Date: 09:12:54 08/31/99
Go up one level in this thread
On August 31, 1999 at 10:46:21, Ricardo Gibert wrote: >On August 31, 1999 at 10:32:10, Robert Hyatt wrote: > >>On August 31, 1999 at 06:16:22, Ralf Elvsén wrote: >> >>>On August 31, 1999 at 04:51:18, Ricardo Gibert wrote: >>> >>>>On August 31, 1999 at 00:30:24, Howard Exner wrote: >>>> >>>>>On August 30, 1999 at 19:41:54, Ralf Elvsén wrote: >>>>> >>>>>>Some while ago I posted a position where I was >>>>>>impressed by Hiarcs accurate evaluation in a pawn ending: >>>>>> >>>>>>6k1/1p4p1/p7/2Ppp3/1P6/P4KP1/5P1P/8 b - - 0 49 >>>>>> >>>>>>The fact that white can create passed pawns on >>>>>>both sides of the board makes the victory clear, >>>>>>and Hiarcs gave an evaluation of about +2. Note however >>>>>>that white is a pawn up. >>>>>> >>>>>>Not being entirely convinced about the >>>>>>impeccabilty of its evaluation, I decided to test >>>>>>some similar "clean" positions. >>>>>> >>>>>>First position: >>>>>> >>>>>>4k3/p6p/8/4p3/3p4/3K4/PP4PP/8 b - - 0 1 >>>>>> >>>>>>This is (from a human point of view) an "identical" position but >>>>>>with material equality. A win for white. Here Hiarcs thinks black >>>>>>is slightly better! >>>>>> >>>>>>Second position: >>>>>> >>>>>>4k3/p6p/8/3p4/2p5/2K5/P4PPP/8 b - - 0 1 >>>>>> >>>>>>Here one pawn is moved from one side of the board to the other >>>>>>(compared to the previous position) and that makes it a clear draw, >>>>>>but Hiarcs thinks white has an advantage, although not decisive. >>>>>>So Hiarcs thinks position 2 is better for white than position 1, >>>>>>when in fact it is worse. >>>>>> >>>>>>I am now inclined to believe (or rather convinced...) >>>>>>that Hiarcs correct score in the position from my >>>>>>original post was due to the fact that white was a pawn up in a pawn ending, >>>>>>(which is heavily weighted, understandably) and not from some accurate >>>>>>evaluation of the pawn structure... >>>>>> >>>>>>Don't investigate the chess "knowledge" of your favourite chess software, >>>>>>your illusions can be shattered :) >>>>>> >>>>>>Ralf >>>>>> >>>>>>PS: I always screw things up when I post positions and other stuff. >>>>>>Hope I got it right this time... >>>>> >>>>>6k1/1p4p1/p7/2Ppp3/1P6/P4KP1/7P/8 b >>>>> >>>>>Here is your original position minus the white pawn on f2, >>>>>so now material is equal. Like Hiarcs' eval of the original >>>>>Rebel 10 also gives a big plus for white. But now in this equal material >>>>>position which remains a very simple win for white, Rebel 10 thinks black is >>>>>much better. It seems that only deep calculation will aid computers here >>>>>while humans see this at a glance. >>>> >>>>Yes. Computers cannot calculate far enough to "understand" these positions. >>>>Their evals are not much better than "random noise". They can do tactics & in >>>>many respects positional play, but stategy (i.e. planning) is neglected, which >>>>is what is needed here. To do stategy, they need to be able to generalize and >>>>they don't do that. >>> >>>I don't know if strategy is needed. As a naive non-programmer >>>I imagine that you could add something like this in the evaluation: >>> >>>local pawn majority (plus check for non-block e.g. >>>white pawns g2, h4, black pawn h5) -> future passed pawn >>> >>>if (the above) on both sides of the board -> big plus in score >>> >>>Of course it depends on the position of the kings etc. >>>Might get messy... I think Bob indicated a scheme similar to this >>>in a previous post (or maybe I misunderstood him). >>> >>>Note that in the last positions I posted, if you let >>>black have pawns on e.g. e4 and d4 and alter the location >>>of the kings slightly, then black can win in some situations... >>> >>>Ralf >> >> >>Note also that there is a special case crafty already handles. IE white >>has pawns at g4/h5 and black has a pawn at h6. White has a 'hidden' passed >>pawn because if he plays g5, he gets a passer immediately that out-runs the >>opponent's passer... > >Writing code for each special cases does not seem practical to me. You may get >some of the more common cases this way, but a more general method is needed to >cope with all of them. I didn't mean to imply I only handle that pawn configuration. A couple of years ago I was watching Roman play Crafty, and he reached a position with pawns on g5/h5 and crafty having a pawn on h7. Crafty was expecting him to play towards pushing g6 to make a passer, which would have been fairly easy to stop. Instead Roman played h6 and crafty's score went _up_ because of the backward pawn now at g5. I later talked to Roman and he mentioned he had seen this many times, and he wanted to know why. I pointed out that crafty thought that g5 was weak. He pointed out that he had a protected passed pawn at h6. Crafty now evaluates "hidden" passed pawns like this anywhere on the board. However, chess is full of exceptions, and this is an exception to backward pawns are bad type rules...
This page took 0.01 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.