Author: Uri Blass
Date: 04:04:40 02/25/04
Go up one level in this thread
On February 25, 2004 at 05:56:16, martin fierz wrote: >On February 24, 2004 at 11:25:23, Robert Hyatt wrote: > >>On February 24, 2004 at 11:17:32, martin fierz 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. :) >>> >>>hehe, i never claimed i wanted 100%. i think your score should reflect the >>>amount of certainty you have. >>> >>>>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. >>> >>>nope. your rule "connected passers are strong when there are many pieces, >>>separated passers when there are few pieces" is good in some cases. but it is >>>not good in quite a lot of cases IMO, with no disrespect to your GM friend. if i >>>make a more accurate version of that rule, i will beat you when it comes up :-) >>> >> >>Perhaps you misunderstood my idea. Connected passers are better when there are >>any pieces on the board. But split passers are better when there are none. I >>just have a smooth transition from one to the other to avoid yet another problem >>called "an evaluation discontinuity".. > >yes, in this case i misunderstood, but i think my misunderstanding is better >than your understanding :-) >connected passers are better with many pieces, split passers are better against >*some* pieces. and of course when there are no pieces left. split passers which >are one file apart are worse than connected passers usually. it all depends on a >lot more than just a one-line-rule... > >i don't know whether i should believe the eval discontinuity thing. i know >somebody recently quoted a paper on this, but it's just a fact: exchanging any >pieces necessarily changes the evaluation. sometimes not by very much. big >changes are usually the exchange of the queen, the exchange of the last rook, >the exchange of the last piece. these eval discontinuities are *real*. i don't >believe in smoothing them out. perhaps if you write an eval with discontinuities >it's harder to get it right that everything fits in with each other, and that's >why it's supposed to be bad?! > > > >> >>The king distance is an easy one to fix. IE my passed pawn race code already >>handles it correctly, in that a pawn can "run" if the king is close enough to >>defend the queening square before the opponent's king can get there, as one >>example of multiple special cases I handle... >> >> >> >>>> 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... >>> >>>that wasn't my point. i assume you are returning a +5 for white even with the >>>black king on e5 and you can lose games where you are completely winning because >>>of this. >> >>Maybe. But most likely not. Wait for my hash collision paper to come out, for >>some _eye-popping_ information about the overall tree search space and how >>resistant to errors it really is. > >it won't pop *my* eyes. i once reduced hash key sizes in my checkers program >beyond all sensible settings, because there was a discussion here about whether >you really need 64-bit keys. in my checkers program, i have 64 bit keys, but >effectively it's only using about 52 bits. i have about a 20 bit part which is >used for the hashindex with %, and of the remaining 44 bits i store only 32 as a >check. i reduced those 32 down to about 8 (!!) bits and in 100 test positions >only saw one different move played IIRC. ridiculous, i must have lots of >collisions there. unfortunately, i didn't count the collision number, or write >down the results - but i know what you're talking about! > >> But that aside, remember that I do a decent >>search as well, _before_ doing static evaluations. If you put the king at e4, >>it doesn't take much of a search to see that black wins, and the eval can't hide >>that because I only evaluate positions reached in the q-search. > >right, if you are already in this position. but there was a position about 12-16 >ply before this, and there you just might have chosen the wrong move because of >this. very, very unlikely, i know. but still... > >cheers > martin > >>> my theory is that you should try to recognize who is winning, but >>>differentiate between being certain that it's a win, and just guessing it's a >>>win. there are very many positions where you can be 99% certain, and for these >>>returning a +5 is ok IMO. for those where it's not so clear, you should guess >>>the result, but only return +1 or so. >>>if you allow a +5 for such positions, you can get into this from a position >>>where you were a piece up, because you simplify to this ending. if you want that >>>to happen, fine :-) >>> >> >>Note that there is an uncertainty in the evaluation. Otherwise wouldn't you >>expect a +9 which is a _real_ queen??? (+8 actually, since the pawn goes and the >>queen appears). > >not necessarily. as a human, i never think in the context of +3 / +5 / +8. in >such situations i think in the context of 99.9% winning probability or not. my >static eval in my brain says "this is unclear" to the type of positions >discussed. if i have a choice of playing this or playing with a piece up and 3 >pawns each for example, i will always choose the piece up position. no margin of >error there... > >cheers > martin I can add that I agree with you in this discussion. Crafty is of course not perfect and can be improved. I also do not like this evaluation of Crafty. I have not complicated evaluation and the main problem is that writing complicated evaluation without bugs is a problem but I have not big scores for unstoppable passed pawns unless they are more advanced than all of the opponent pawns. Today I even do not evaluate unstoppable passed pawns that are not more advanced than all of the opponent pawns. Uri
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