Author: Robert Hyatt
Date: 15:00:32 02/27/00
Go up one level in this thread
On February 27, 2000 at 14:03:11, Richard A. Fowell (fowell@netcom.com) wrote: >On February 27, 2000 at 11:19:04, Daniel Clausen wrote: > >>Hi >> >>On February 27, 2000 at 00:15:14, Richard A. Fowell (fowell@netcom.com) wrote: >> >>>I noticed today that six of the seven chess programs that I tried >>>(three freeware, four commercial) failed to pass the two tests below. >>> >>>(my congratulations to Will Bryant, who programmed Screamer right!) >>> >>>The others don't understand how castling rights and en passant capture >>>rights effect the ability to claim draw by three-fold repetition of position. >>> >>>The FIDE Laws of Chess (1997, but unchanged from when I learned chess 26 years >>>ago) say: >> >>[snip] >>>#1 Check for knowledge of castling rights on triple repetition draw = >>> >>>1. Nf3 Nf6 >>>2. Rg1 Rg8 >>>3. Rh1 Rh8 (second occurrence of this visible piece pattern, but first >>>occurrence w/o castling rights) >>>4. Rg1 Rg8 >>>5. Rh1 Rh8 ( No draw, yet - this is the original piece pattern, but there >>> both sides had castling rights. To put it another way, the EPD >>> strings for the starting position and this one are different.) >>>6. Rg1 Rg8 - draw by triple repetition of position. >>> >>>#2 Check for knowledge of en passant opportunity of triple repetition draw = >>> >>>1. a4 a6 >>>2. a5 b4 [ This should be b5, as sargon points out. - Richard ] >>>3. Nf3 Nf6 >>>4. Ng1 Ng8 (second occurrence of this visible piece pattern, but first >>>occurrence w/o en passant capture option) >>>5. Nf3 Nf6 >>>6. Ng1 Ng8 (again, no draw yet - there is no en passant capture possible here, >>> as there was after Black's second move). >>>7. Nf3 - draw by triple repetition of position. >> >>>Which chess programs (other than Screamer) get these right? >> >>Not that anyone cares, but my engine gets these right. :) > >Actually, I care - for two reasons. First, it is nice to think that I'm >not the only one to think it is worth doing this right. Second, it might >help other programmers address this if those who do handle this could >present a simple way of doing so. > >So - what do you use? Robert Hyatt says he includes castling rights/en passant >in his hash. Is that what you do? I would hope that _everybody_ includes castling/EP status in their hash signature. Not doing so invites a tremendous number of false matches that will certainly affect play. Whether they use the hash signature for repetition is another subject, although I would suspect it to be very common. But if it is, then someone has a serious problem since you said several failed your test, which implies that the castle/ EP status is not handled correctly. I don't believe this can be safely overlooked, because the wrong repetition value is a tiny part of a much bigger problem, that of not correctly hashing positions... the former may not happen often. The latter happens thousands of times every search. Often enough that it will _definitely_ affect the root score enough to make a difference. > > >>But only >>if blacks 2nd move in the 2nd mini-game is b5. (instead of b4) >> > > Quite right - too many years of descriptive notation for me, I fear. >>Kind regards, >> -sargon
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