Author: Robert Hyatt
Date: 08:04:38 09/19/01
Go up one level in this thread
On September 19, 2001 at 10:16:36, Uri Blass wrote: >On September 19, 2001 at 09:52:52, Robert Hyatt wrote: > >>On September 19, 2001 at 05:20:31, Bernhard Bauer wrote: >> >>>>>>>Here is a simple attempt: >>>>>>> >>>>>>>[D]2k5/1r6/3p1p2/n2p1p2/P2PpP2/R3P3/1BK5/8 b - - >>>>>>> >>>>>>>Here black has several moves to try, one which liquidates into a pawn up >>>>>>>(but dead lost) ending. Rxb2 Kxb2 Nc4+ Ka2 Nxa3 Kxa3 and white is a pawn >>>>>>>down, but winning easily. >>>>>>> >>>>>>>Once you start with Rxb2, you are committed. As if you try to back out and >>>>>>>not play Nc4 and Nxa3, you are an exchange down. And if you do recover the >>>>>>>material, you are dead lost. Add another such forced capture/recapture and >>>>>>>you have burned 6 plies. You won't see white winning all the black pawns >>>>>>>and winning. >>>>>> >>>>>> >>>>>>Note that I don't say there are not better moves for black here. The point >>>>>>was to show a move choice that commits you to a course of action that gets >>>>>>worse and worse as you go deeper and deeper. >>>>> >>>>>I think that this is not a good example because white has an obvious positional >>>>>advantage for programs(white has a passed pawn when black has 2 pawns on the >>>>>same file for file d,f >>>>> >>>>>Uri >>>> >>>> >>>>Pick any such position you want, where one side is a pawn up but the other is >>>>winning. I have seen many. That is one example where if you trade, you lose. >>>>And it is one example of where one extra pawn does _not_ mean you are winning. >>>>Here it means you are losing and badly. >>>> >>> >>>From a players point of view *white*is a pawn up, the a-pawn and therefor >>>winning, just like Ed said. >>>A player would not count the additional blocked black pawns. >>>Kind regards >>>Bernhard >> >> >>Human, right. But set the position up and ask your favorite program which side >>is winning with a simple static eval... > >I asked few program to give me their evaluation at depth 1 for this position >[D]2k5/8/3p1p2/3p1p2/P2PpP2/n3P3/K7/8 w - - 0 3 > > >CometB27 0.53 for white >Junior7 0.20 for black. >shredder5.32 0.18 for black. > >They clearly can see white's positional advantage by static evaluation and do >not give +1 for black. The two commercial programs say black is better. White is winning. You don't see a problem with that kind of incorrect evaluation? IE as black they would go for this position rather than a repetition draw. That was my point. If you say "a pawn ahead is winning" you are going to lose many games by doing so. Particularly when your opponent notices that you are doing this and steers the game into such positions. I will be happy to give you a similar position where the pawns are not isolated if you think that is the problem... Keep the pieces at the same squares. Pub black pawns at h7, g6, e7 and d6. put white pawns at g5, d5 and a4. What does your engines think now? Black is a pawn up. no isolated pawns... black loses by trading off the pieces. Draws (or possibly wins) by keeping the pieces on. trading down when a pawn ahead is a wrong rule. In my code, the outside passer, or outside candidate grows in value as pieces come off, so that Crafty at least has a basic understanding for when to trade and when to avoid trades. It _certainly_ isn't dependent on just counting the white and black pawns. In fact, they don't affect that part of the score at all, other than crafty wants more pawns and fewer pieces in such positions, rather than more pieces and fewer pawns. > >I said that it is usually safe to evaluate as +2 >pawn endgames when programs cannot see positional advantage for the side with >less pawns. > >This is not the case in this example. > >Uri
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