Author: Robert Hyatt
Date: 08:37:58 02/24/04
Go up one level in this thread
On February 24, 2004 at 11:12:57, Bob Durrett wrote: >On February 24, 2004 at 11:06:00, Robert Hyatt wrote: > >>On February 24, 2004 at 10:37:21, martin fierz wrote: >> >>>On February 24, 2004 at 10:19:51, Anthony Cozzie wrote: >>> >>>>On February 24, 2004 at 09:32:08, martin fierz wrote: >>>> >>>>>On February 23, 2004 at 23:05:58, Robert Hyatt wrote: >>>>> >>>>>>On February 23, 2004 at 18:52:36, Geoff Westwood wrote: >>>>>> >>>>>>>Hi >>>>>>> >>>>>>>I was perusing the latest table of results, Crafty's static eval of 2 of the >>>>>>>passed pawn positions were interesting. >>>>>>> >>>>>>>Assuming I havent made a mistake in the cutting and pasting >>>>>>> >>>>>>>Position 1 >>>>>>>8/4k3/8/7P/1P6/3p4/4p3/4K3 b - -; id "PP-00004" >>>>>>> >>>>>>>[D]8/4k3/8/7P/1P6/3p4/4p3/4K3 b - - >>>>>>> >>>>>>>Crafty reckons this is +4.8 (good for white). This is rather clever as although >>>>>>>the black king could catch either of the white passed pawns, it cannot stop >>>>>>>both. Also blacks 2 advanced pawns cant do anything as the white king gobbles >>>>>>>them up easily. Only Crafty and Tinker understand this position statically. Any >>>>>>>tips on what the algorithm is to sort this one out ? >>>>>> >>>>>> >>>>>>This is the idea I have reported here before, pointed out (demanded to be fixed >>>>>>in fact) by a GM friend of mine. The idea is that the two separated pawns are >>>>>>better than the two connected passers. The king stops the two connected passers >>>>>>easily until the enemy king supports them, meanwhile the split passers walk on >>>>>>in... >>>>> >>>>>i don't like the generality of your statemtent here, but - it is a small price >>>>>to pay if it's right in most cases. which perhaps is the case. anyway, here's my >>>>>question: >>>>> >>>>>what does your static eval say for the black king on e6/e5/e4/e3 ? i wouldn't be >>>>>surprised if it got it wrong in some cases now... >>>>> >>>>>cheers >>>>> martin >>>> >>>>The question is always "what do you put in the search, what do you put in the >>>>eval" <shrug>. >>> >>>sort of - for me the answer is clear. the point i wanted to make (not the first >>>time, BTW) is that returning huge evaluations in positions like this may not be >>>a good idea because they are *very* sensitive to details like king position. >>>e.g. if i got it right, then it's a white win with the king on e6, but a black >>>win with the king on e5. do you really want to allow your static eval to return >>>a white win when it might be a black win? >>>of course you can say that if you get it right 60% of the time, it is better >>>than returning an equal eval in this kind of position. but wouldn't it be better >>>then to return something like +- 1 so that you never blunder into this when you >>>are e.g. a piece up and see this type of transition? >>>i generally try to return huge evals only when i am very certain that they are >>>correct. >>> >>>cheers >>> martin >> >>You are looking at this the wrong way. If you want 100% accuracy, you will die >>from it. :) >> >>If you don't do what I do, you will like connected passers, and in 90% of the >>games I will beat you when that comes up. Do you want to be right 100% of the >>cases you recognize, leaving 95% as "unclear and probably lost" or do you want >>to be right in 90% of the total cases? >> >>I choose the latter... >> >>No doubt it can be made more accurate. But no doubt that without it, it is even >>less accurate... > >Why not get rid of bugs when you know about them? > >Bob D. I always do. However, this is not simply an evaluation problem. :) I should add that there are two eval components involved here. The "split" vs "connected" passer code is not significant here. That is about 1/2 pawn total. The problem in _this_ position is that white has an unstoppable passer, because he has two, and whichever black tries to stop, white runs in with the other. This is a variation of the "square of the pawn" rule for king and pawn endings. In this special case, it is right until the king is so far advanced that the black pawns can't promote because of black's mate threat with the king and two pawns. I had mistakenly introduced the "noise" about the split passer code when I was looking at it, because that code is there solely to make sure that I don't consider the two connected passers to be better than two separated passers, and lose quickly in most cases. In this position, the question the eval asks is "does the opponent have an unstoppable passer". With the king at e4, for example, white's h-pawn will promote and there is nothing black can do about it. Except mount a mate threat which the evaluation is not supposed to handle. Here I have to depend on the knowledge about the pawn promoting being overridden by the search that finds the mate threat prevents the promotion. > > >> >> >>> >>>>I have considered trying to do a really good KP eval; at the moment it is on the >>>>back-burner but I might return to it someday. >>>> >>>>anthony
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