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Robert Hyatt

Joined: 27 Feb 2006
Posts: 15818
Location: Birmingham, AL

Post subject: Re: Comparative nodes per second    Posted: Tue Apr 17, 2012 7:59 pm

BubbaTough wrote:
bob wrote:
BubbaTough wrote:
 Don wrote: I think you are saying that this exact position is one that an evaluation function should try to evaluate and I don't know why you think we disagree - I didn't say one way or other about whether you should try. In Komodo we try to do special evaluation when we think we can do it reliably. I don't really know if you can do that position reliably or not. Maybe you can but you didn't specify what class of positions you are talking about. If you mean that EXACT position then it's easy to evaluate, just test for it and score it as a win if you get an exact match. So you have to specify what specifically is it in that position that you think you can reliably evaluate. Do you mean any position where there is a pawn on the 7th and the opponent doesn't have a pawn on the 7th? What rule covers that STATICALLY without a search? What if the side with the pawn on the 7th can be mated immediately? Now if you impose too many constraints, you make the rule almost useless. In fact Larry and I decided to work on square of the pawn a while back and we had a very difficult time coming up with RELIABLE rules! We kept adding constraints so that we would not score a win if there was some doubt but after some time we discovered that it's not possible to make this rule perfect, and in fact the harder we tried, the less often the rule could even be used. So this simple rule, to really get right, requires a large decision tree with all sorts of rules - the type of thing you usually don't want to put in a chess program. Anyway, propose a generally applicable rule that applies to this position and many others and let's see if it's simple or not. What are your rules?

The rule is, 2 connected passed pawns on the 6th (or 7th) can force a queen against a rook if the king is not close enough. Like the square of the pawn rule, you can find situations where it is not a win, but, like the square of the pawn rule, it is winning enough of the time that it is worth using search to find the exceptions rather than to use search to replicate its findings.

Its not uncommon for strong players to sacrifice if they see they can get 2 pawns on the 6th against a rook, without bothering to calculate much further.

-Sam

I think it is dangerous to assume a win and let the search find a refutation if one exists. A deep / wide search can use (still) the horizon effect to its advantage here to cause embarrassing moves in real games. I trust the search more than the eval when we are talking about races, checks, interference squares and such. I suppose it boils down to how much error, and where, are you willing to tolerate?

I think it really only boils down to which is more accurate, more often. If you look up rook vs. 2 connected passed on the 6th in Dvoretsky's endgame manual, you will see all sorts of tricks showing the rook finding a draw against the pawns. But these are really just exceptions to the rule. In a vast majority of cases the pawns win. VAST majority. And I find it embarrassing in real games to miss these, which is a risk if you prune a lot. Any statement like "I suppose it boils down to how much error, and where, are you willing to tolerate?" can always be turned on it head. How much error in your Eval's assumption that the rook is better than the pawns are YOU willing to tolerate, given the embarrassing moves relying on your search may lead you to?

-Sam

After my experiences (bad) with two connected passers on 6th vs rook, I simply want to let the search discover something good, rather than depending on it to discover something bad. Where the eval gets it wrong in a fast game, I might be stuck with that. In the majority of cases, two connected passers on the 6th are not better than a rook. Unless you tightly constrain it such as "opponent ONLY has a rook, king is at LEAST N squares away, King is not hemmed in and subject to perpetual by the rook, and is not getting mated." I'd prefer to avoid quick searches that push the pawns to the 6th, dropping a pair of bishops or something in the process, and assume it is winning...

Won't begin to argue my approach is the right one, just that it is "my approach" here after getting burned a few times on ICC with that connected on 6th eval term.
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Subject Author Date/Time
Larry Kaufman Tue Apr 10, 2012 7:49 pm
Vincent Diepeveen Tue Apr 10, 2012 8:16 pm
Marco Costalba Tue Apr 10, 2012 8:41 pm
Larry Kaufman Tue Apr 10, 2012 9:02 pm
Thomas Petzke Tue Apr 10, 2012 9:30 pm
Richard Vida Tue Apr 10, 2012 10:15 pm
Larry Kaufman Tue Apr 10, 2012 10:18 pm
Sam Hamilton Tue Apr 10, 2012 10:54 pm
Richard Vida Tue Apr 10, 2012 11:28 pm
Larry Kaufman Wed Apr 11, 2012 4:52 am
Don Dailey Wed Apr 11, 2012 11:23 pm
Don Dailey Wed Apr 11, 2012 11:50 pm
Sam Hamilton Thu Apr 12, 2012 12:07 am
Robert Hyatt Tue Apr 10, 2012 9:31 pm
Larry Kaufman Tue Apr 10, 2012 9:35 pm
Robert Hyatt Thu Apr 12, 2012 1:10 am
Daniel Shawul Tue Apr 10, 2012 11:41 pm
Larry Kaufman Wed Apr 11, 2012 5:05 am
Sam Hamilton Wed Apr 11, 2012 5:28 am
Marco Costalba Wed Apr 11, 2012 5:58 am
Larry Kaufman Wed Apr 11, 2012 1:04 pm
Daniel Shawul Wed Apr 11, 2012 12:27 pm
Jon Dart Wed Apr 11, 2012 1:59 pm
Sam Hamilton Wed Apr 11, 2012 2:25 pm
Larry Kaufman Wed Apr 11, 2012 2:36 pm
Jon Dart Wed Apr 11, 2012 3:06 pm
Larry Kaufman Wed Apr 11, 2012 2:28 pm
Jon Dart Wed Apr 11, 2012 3:10 pm
Larry Kaufman Wed Apr 11, 2012 3:59 pm
Robert Hyatt Thu Apr 12, 2012 1:19 am
Robert Hyatt Thu Apr 12, 2012 1:15 am
Larry Kaufman Thu Apr 12, 2012 1:35 am
Sam Hamilton Thu Apr 12, 2012 2:32 am
Larry Kaufman Thu Apr 12, 2012 2:50 am
Sam Hamilton Thu Apr 12, 2012 3:10 am
Larry Kaufman Thu Apr 12, 2012 3:35 am
Jon Dart Thu Apr 12, 2012 2:37 pm
Larry Kaufman Thu Apr 12, 2012 3:24 pm
Jon Dart Thu Apr 12, 2012 4:25 pm
Don Dailey Thu Apr 12, 2012 4:33 pm
Jon Dart Thu Apr 12, 2012 4:41 pm
Robert Hyatt Thu Apr 12, 2012 8:13 pm
Robert Hyatt Thu Apr 12, 2012 9:00 pm
Daniel Homan Thu Apr 12, 2012 9:52 pm
Robert Hyatt Thu Apr 12, 2012 11:26 pm
Larry Kaufman Thu Apr 12, 2012 11:40 pm
Sam Hamilton Thu Apr 12, 2012 11:51 pm
Robert Hyatt Sat Apr 14, 2012 4:23 am
Uri Blass Sat Apr 14, 2012 5:05 pm
Robert Hyatt Sat Apr 14, 2012 6:46 pm
Don Dailey Sat Apr 14, 2012 6:56 pm
Robert Hyatt Sun Apr 15, 2012 4:31 am
Larry Kaufman Sat Apr 14, 2012 7:47 pm
Robert Hyatt Sun Apr 15, 2012 4:36 am
Larry Kaufman Sun Apr 15, 2012 4:47 am
Robert Hyatt Mon Apr 16, 2012 7:14 pm
Robert Hyatt Tue Apr 17, 2012 3:02 pm
Robert Hyatt Thu Apr 12, 2012 6:50 pm
Larry Kaufman Thu Apr 12, 2012 8:12 pm
Robert Hyatt Sat Apr 14, 2012 4:28 am
Larry Kaufman Sat Apr 14, 2012 4:45 am
Robert Hyatt Sat Apr 14, 2012 4:46 pm
Larry Kaufman Sat Apr 14, 2012 5:10 pm
Sam Hamilton Sat Apr 14, 2012 5:35 pm
Robert Hyatt Sun Apr 15, 2012 4:38 am
Larry Kaufman Sun Apr 15, 2012 4:51 am
Robert Hyatt Mon Apr 16, 2012 7:20 pm
Don Dailey Sun Apr 15, 2012 12:14 pm
Robert Hyatt Mon Apr 16, 2012 7:21 pm
Uri Blass Sat Apr 14, 2012 5:17 pm
Larry Kaufman Sat Apr 14, 2012 5:22 pm
Uri Blass Sat Apr 14, 2012 5:36 pm
Larry Kaufman Sat Apr 14, 2012 5:47 pm
Sam Hamilton Thu Apr 12, 2012 4:49 pm
Larry Kaufman Thu Apr 12, 2012 5:14 pm
Jon Dart Thu Apr 12, 2012 6:00 pm
Uri Blass Thu Apr 12, 2012 6:37 pm
Jon Dart Thu Apr 12, 2012 6:50 pm
Uri Blass Thu Apr 12, 2012 6:53 pm
Lucas Braesch Sun Apr 15, 2012 4:56 am
Uri Blass Sun Apr 15, 2012 5:16 am
Lucas Braesch Sun Apr 15, 2012 7:58 am
Don Dailey Sun Apr 15, 2012 1:10 pm
Uri Blass Sun Apr 15, 2012 2:48 pm
Don Dailey Sun Apr 15, 2012 3:26 pm
Robert Hyatt Tue Apr 17, 2012 5:17 pm
Sam Hamilton Tue Apr 17, 2012 6:05 pm
Robert Hyatt Tue Apr 17, 2012 7:11 pm
Don Dailey Tue Apr 17, 2012 6:06 pm
Sam Hamilton Tue Apr 17, 2012 6:16 pm
Don Dailey Tue Apr 17, 2012 6:45 pm
Sam Hamilton Tue Apr 17, 2012 6:55 pm
Robert Hyatt Tue Apr 17, 2012 7:16 pm
Sam Hamilton Tue Apr 17, 2012 7:25 pm
Re: Comparative nodes per second Robert Hyatt Tue Apr 17, 2012 7:59 pm
Sam Hamilton Tue Apr 17, 2012 8:14 pm
Miguel A. Ballicora Tue Apr 17, 2012 10:33 pm
Sam Hamilton Tue Apr 17, 2012 10:51 pm
Vincent Diepeveen Wed Apr 18, 2012 12:12 am
Sam Hamilton Wed Apr 18, 2012 12:28 am
Miguel A. Ballicora Wed Apr 18, 2012 2:28 am
Sam Hamilton Wed Apr 18, 2012 4:32 am
Miguel A. Ballicora Wed Apr 18, 2012 4:44 am
Miguel A. Ballicora Tue Apr 17, 2012 10:28 pm
José C. Martínez Galán Wed Apr 18, 2012 6:16 am
Robert Hyatt Thu Apr 19, 2012 9:53 pm
Don Dailey Thu Apr 19, 2012 10:22 pm
José C. Martínez Galán Thu Apr 19, 2012 10:49 pm
Robert Hyatt Thu Apr 19, 2012 11:21 pm
Marco Costalba Fri Apr 20, 2012 5:18 am
Michel Van den Bergh Fri Apr 20, 2012 6:10 am
Miguel A. Ballicora Fri Apr 20, 2012 11:35 am
Don Dailey Fri Apr 20, 2012 10:57 am
Marco Costalba Fri Apr 20, 2012 1:58 pm
Sam Hamilton Fri Apr 20, 2012 2:19 pm
Miguel A. Ballicora Fri Apr 20, 2012 2:29 pm
Don Dailey Fri Apr 20, 2012 3:13 pm
Don Dailey Fri Apr 20, 2012 4:52 pm
Uri Blass Sat Apr 21, 2012 6:03 am
Marco Costalba Sat Apr 21, 2012 8:14 am
Ed Schroder Sat Apr 21, 2012 10:50 am
Marco Costalba Sat Apr 21, 2012 11:13 am
Don Dailey Fri Apr 20, 2012 12:31 pm
Dan Andersson Fri Apr 20, 2012 4:14 pm
Don Dailey Fri Apr 20, 2012 4:38 pm
Robert Hyatt Thu Apr 12, 2012 7:10 pm
Robert Hyatt Thu Apr 12, 2012 6:55 pm
Robert Hyatt Thu Apr 12, 2012 7:36 pm
Robert Hyatt Thu Apr 12, 2012 7:13 pm
Larry Kaufman Thu Apr 12, 2012 8:18 pm
Robert Hyatt Thu Apr 12, 2012 8:55 pm

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