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...BubbaTough wrote: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?bob wrote: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?BubbaTough wrote: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.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?
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
-Sam
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.
. Note, its very very very rare for this to be a win for the rook, so its darn safe to assume the pawns are work AT LEAST a rook.