Author: Robert Hyatt
Date: 11:05:53 11/27/03
Go up one level in this thread
On November 26, 2003 at 23:45:47, Uri Blass wrote: >On November 26, 2003 at 23:15:57, Robert Hyatt wrote: > >>On November 26, 2003 at 22:12:43, Uri Blass wrote: >> >>>On November 26, 2003 at 21:14:14, Robert Hyatt wrote: >>> >>>>On November 26, 2003 at 20:20:26, Peter Berger wrote: >>>> >>>>>For information about setup and rules: >>>>>http://www.talkchess.com/forums/1/message.html?329237 >>>>> >>>>>Looks strangely familiar? - yes, the controversial setup of game 2 again. Space >>>>>advantage vs. pawn - OK, nothing new, we get this in every other game. >>>>> >>>>>This time after the "novelty" 27. Nf4 Junior reached less than nothing - it's >>>>>just too drawish. >>>>> >>>>>In 1985 there was some upset in our little rural chessclub - a computer had >>>>>proven hat KRBKR was a forced win, amazing. Dunno how this came up, and of >>>>>course these days we know better - many if not most of these positions are a >>>>>draw. >>>>> >>>>>But surely not all of them - KRBKR is dangerous to the extreme, especially if >>>>>the defending king is restricted to the back row - Crafty deals with these >>>>>positions as a draw statically in general (my humble and very possibly wrong >>>>>judgement after watching the game and evals , no analysis of source coude ) - >>>>>dary judgement by the engine. >>>>> >>>>>Not to have to deal with general criticism about setup I spent quite some time >>>>>tonight with the best and fastest computer I could come up with in analysis - of >>>>>course with all the 5-piece tablebases, to make sure the problem is for real. >>>>> >>>>>It is - Crafty is not aware that KRBKR is just mean, even with 5 piece >>>>>tablebases, something very similar (identical in fact) to the actual game would >>>>>have happened. >>>> >>>>I will look, but two things. If it ended up in a lost KRB vs KR, that can >>>>happen. But if it has tables it will likely _not_ end up in that position >>>>as it would avoid trading down to it... >>> >>>The problem was losing KRB vs KRPP based on looking in the game. >>> >>>I am not sure about the losing mistake of Crafty but I think it was Rh1 in the >>>following position >>> >>>[D]5k2/7R/7p/p3K3/2B5/8/8/5r2 b - - 0 64 >>> >>>> >>>>That's the purpose of tables. >>>> >>>>Losing the occasional KRB vs KR is not something I worry about, because most >>>>all chess program users have at least the full 5-piece set of tables which >>>>avoids 99.9% of the problems, where KRB vs KR is won is a very tiny percentage >>>>of all KRB vs KR endings... >>>> >>>>When you say something "identical" would have happened with the tables, you >>>>overlook the power of probing the tables _deep_ in the search, so you simply >>>>don't trade into such lost positions... Crafty doesn't trade into such a >>>>position and _then_ realize "crap, lost position, shouldn't have done that." >>>> >>>>That's why the tables are important. >>>> >>>>Here, if a program thinks KRB vs KR is winning, it will be wrong most >>>>of the time. You look _really_ silly winning a piece, trading your last >>>>pawn, to end up in a nearly forced draw with KRB vs KR. >>> >>>Junior did not evaluate it as winning a piece but evaluated it as advantage for >>>the side with the bishop(I am sure that Junior could see by search at least >>>winning one pawn to get KRB vs KRP but Junior never evaluated it as something >>>close to +2 and the evaluation was +0.5 or +0.8 in most of the endgame). >>> >>>Uri >> >> >>It was _still_ wrong. In KRB vs KRP, in 99% of the cases, KRP draws or >>wins. Thinking the KRB side is better is simply wrong. > >I think that evaluation is dependent on the position and KRB vs KRP is not >enough information. > >winning for the pawn can happen only if the pawn is very advanced(otherwise the >bishop can sacrifice itself for the pawn for a draw) so it is clear that in the >relevant position there were only chances for the bishop. > >The fact that the opponent king was in the last rank also helped to increase the >chances. > >It is not the first case when I see that KRB wins KRP in comp-comp games. > > > Except for the >>rare exception. I suspect Crafty with tables might well avoid the critical >>trade but I am not sure, some are very deep. >> >>But I'll take the occasional loss for being wrong, just as I accept the >>occasional case where I don't take the trojan horse but should. It was >>wrong here (Crafty). But it is right _most_ of the time. A program that >>thinks KRB vs KR or KRP, or KRN vs KR or KRp, is better for the KRB or KRN >>is going to be wrong most of the time. Look at the KRB vs KR tablebase >>summary file... > >Statistic about KRB vs KR is not relevant because the position that heppens in >the board is not random KRB vs KR position. > >Uri Actually it is, when you think about it. This same thing could have happened with the black king anywhere on the board and white and black would have evaluated it the _same_ way, and white would not have won most of those cases.
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