Author: Robert Hyatt
Date: 14:20:20 10/04/01
Go up one level in this thread
On October 04, 2001 at 14:59:39, Paul wrote: >On October 04, 2001 at 14:19:03, Robert Hyatt wrote: > >>On October 04, 2001 at 10:55:32, Paul wrote: >> >>>On October 04, 2001 at 10:41:30, Tim Foden wrote: >>> >>>>On October 04, 2001 at 10:11:36, Paul wrote: >>>> >>>>>On October 04, 2001 at 07:03:14, Tim Foden wrote: >>>>> >>>>>>Hi All, >>>>>> >>>>>>I decided that I would add a 2nd SEE to GLC to check whether GLC's SEE was >>>>>>working. I actually ported GCP's Sjeng SEE (that was posted to the forum a >>>>>>while ago). >>>>>> >>>>>>Both SEE routines now agree in most curcumstances, but one's like the following >>>>>>have cropped up (where they disagree): >>>>>> >>>>>>[D]5rk1/1pp2R1p/p1pb4/6q1/3P1p2/2P4r/PP1BQ1P1/5RKN w - - 2 0 >>>>>> >>>>>>This can be evaluated in 2 ways... >>>>>> >>>>>>(1) BxP (+1000) BxB (-3500) R1xB (+3500) QxR (-5500) RxQ (+10000) RxR (-5500) >>>>>>.........+1000.......-2500........+1000.......-4500........+5500...........0 >>>>>> >>>>>>>>> value = 0 >>>>>> >>>>>>(2) BxP (+1000) BxB (-3500) R7xB (+3500) RxR (-5500) RxR (+5500) QxR (-5500) >>>>>>.........+1000.......-2500........+1000.......-4500.......+1000.......-4500 >>>>>> >>>>>>>>> value = -2500 >>>>>> >>>>>>So... on to the questions: >>>>>> >>>>>>a) Does anyone's SEE do anything intelligent in these cases? >>>>>> >>>>>>b) Is one of these right, and the other wrong? If so, which one? >>>>>> >>>>>>c) Do we actually care, as long as the SEE works in the majority of cases? >>>>>> >>>>>>Cheers, Tim. >>>>> >>>>>I haven't studied SEE yet, but shouldn't (2) also result in a value = 0, since >>>>>you don't have to take the pawn being white? I mean, you start with a value of >>>>>0, right? >>>> >>>>Yes, you start with a value of 0. In this particular case I think that (1) >>>>above is best. But should a SEE routine care? I mean... maybe this kind of >>>>thing doesn't occur often enough to worry about. I'm not sure about this, so >>>>I'm asking questions to see if anyone else has a better idea. >>>> >>>>Cheers, Tim. >>> >>>No, I guess I didn't make myself clear ... I meant: why do you say value=-2500 >>>in case (2) and not value=0? I thought that SEE worked in such a way that you: >>> >>>(a) play out all the captures for both sides to the end, and then >>>(b) work your way back to the front to see where each should stop capturing to >>> max its own result. >>> >>>Now if you do that for white in case (2), shouldn't (b) result in white not >>>capturing anything and so value=0? >>> >>>Hope you can point out where I go totally wrong. :) >>> >>>Groetjes, >>>Paul >> >> >>The point here is that you are asking, in the program "does taking this pawn >>win, lose, or break even?" If the answer is "lose" then you don't make the >>capture at all. If the answer is win, you always make it. If the answer is >>break even you can do what you want. You are correct that taking the pawn is >>not forced here. My SEE works as he explained. It assumes that you _must_ >>take the pawn, and tells you whether you win, lose or break even. You use that >>do decide whether to _actually_ take it or not. > >I understand, but this is all new to me so please bear with me. > >Now suppose the capture on f4 is beneficial for white, so you capture with white >and do a recursive call to Quiescence(). You generate a new list of capturing >moves, and while iterating through this list at a certain moment you're going to >be faced with captures to & SEE calculations for the f4 square. > >But you've just done that calculation 1 ply up and that said it was good for >white, so this time it has to be bad for black. Consequently you don't even have >to do any SEE calculations for f4 captures at this ply, and can discard any >captures to f4 immediately? > >Does this mean that once you've done a capture on a square, you can ignore all >captures to that square one ply deeper? > >Paul No. We are just using the SEE score to order the possible captures at any ply in the q-search. If SEE says a capture loses material, I don't even consider the capture in Crafty's q-search, for example.
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