Author: Vasik Rajlich
Date: 04:12:37 05/06/04
Go up one level in this thread
On May 06, 2004 at 05:24:29, Tord Romstad wrote: >On May 05, 2004 at 14:35:10, Vasik Rajlich wrote: > >>Well, for KQKR I'm sure you can in a few hours come up with something effective, >>even at low search depths. However, for things like KRPKR and KPPKP, tablebases >>are a really nice solution that you won't easily replace. > >It's funny that you bring up KRPKR as an example, because I already have a >specialized KRPKR eval which works reasonably well in practise. It recognizes >some of the most basic won or drawn positions (including the Philidor and >Lucena positions), and also has some of the heuristic knowledge you will find >in rook endgame books (king on the short side, rook on the long side, using >the rook to cut off the defending king, etc.). It is nowhere near perfect, >but it is good enough to have saved a huge number of half points against >other engines in my test matches. Do you mean that if you pass just about any KRPKR endgame to your evaluation function, it will return a score of either 0.0 or +/- MAX_SCORE? I think this is what you want (ideally). If you're doing this, then you better be really sure that you're right. Eventually I hope to have my evaluation do something close to this with more complex endings. Apparently it's not so easy though. Even Shredder and Fritz have the problem of transitioning an advantage into a drawish (or even drawn) ending, while still giving big scores. KPPKP by the way would be next-to-impossible to do with heuristics, although at least this will happen much less in practice than KRPKR. > >Implementing it took a few days rather than a few hours, though. > >>Note also that 20 elo points is nothing to scoff at. > >Perhaps not, but 20 Elo points is a *very* generous estimate of the >improvement provided by tablebases. The data I have seen indicate that >the strength improvement is hardly noticable. > >>If you speed up your engine >>by 40%, that's about what you'll gain, and we've seen how far some people will >>go to get this. You're probably at the point with Gothmog where you'll happily >>work for a month to get a ten-point increase. > >A "month" is not a very precisely defined term when it comes to chess >programming. Like all other amateurs, I don't always have the opportunity >to work equally much. During some months, I hardly find any time to program >at all, but it also happens that I work 10 or 15 hours per month. With >something like 15 hours of programming and 20 days of CPU time, a ten-point >increase isn't hard to achieve with an engine at Gothmog's level. There >are so many pieces of missing knowledge, so many search and eval weights to >tune, and so many stupid bugs to fix. > Hmmm. I'm skeptical, 10 points in fifteen hours is quite a bit. I'm getting much less than that with Rybka. (Although a lot of my work is still on infrastructure and testing procedures, so it's hard to give a fair #.) BTW I've been including Gothmog in my gauntlets, and against Rybka it scores slightly better than Crafty and Pepito (but not as well as Fritz 5.32 or Ruffian). I think it's for the same reason that Shredder 8 scores about 100 points better than Fritz 8 - Rybka's search is better than its eval, so it's more vulnerable to king attacks. >>Re. the aesthetics, you can also think of tablebases as far more general than >>any heuristics you'll come up with to replace them. The tablebase code knows >>only about mates and draws, and its search figures out the rest. It's just an >>implementation detail that you precompute the results. :-) > >It is not entirely accurate to say that I precompute the results. The >results have been precomputed by Nalimov's code, which I don't even >understand myself. This is another reason why I prefer not to use TBs. > Well, ok, aesthetics are aesthetics. I could argue that you happily use a compiler, which also does all sorts of things you don't understand. :-) Vas >Tord
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