Author: Will Singleton
Date: 16:10:44 01/29/01
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On January 26, 2001 at 09:41:51, Robert Hyatt wrote: >On January 26, 2001 at 01:16:37, Will Singleton wrote: > >>On January 26, 2001 at 00:06:31, Robert Hyatt wrote: >> >>>On January 25, 2001 at 23:49:07, Robert Hyatt wrote: >>> >>>>On January 25, 2001 at 21:35:10, Will Singleton wrote: >>>> >>>>>On January 25, 2001 at 09:41:41, Robert Hyatt wrote: >>>>> >>>>>>On January 25, 2001 at 00:16:04, Andrew Dados wrote: >>>>>> >>>>>>>Thanks Bob for very interesting report. >>>>>>>A couple of loose thoughts... >>>>>>> >>>>>>>Recapture extension is intuitively no good for tactical suite for a simple >>>>>>>reason: all tactical lines give up temporarily material. And lines with >>>>>>>exchanging down pieces are not 'beautiful' for humans - which was probably one >>>>>>>of conditions for selecting a 'tactical' position into set like WAC. >>>>>>> >>>>>>>It is hard to say if your program plays weaker or stronger in practical games >>>>>>>because of it. And, btw, one of Craftys strengths is exchanging down to won >>>>>>>endgame. Maybe some sort of nunn-type match between 2 versions can give more >>>>>>>data about it? >>>>>>> >>>>>>>And if you come down to think about the trend - It would be interesting to run >>>>>>>your test with recapture extension going below zero....:) >>>>>>> >>>>>>>-Andrew- >>>>>> >>>>>>Ken Thompson got me started on this in the early 80's. The idea is that >>>>>>if you are in some kind of trouble (say losing a pawn) then one way to help >>>>>>"hide" this is the good old BxN PxB sequence. BxN forced the opponent to >>>>>>recapture the bishop, and that eats two plies of your total search, maybe >>>>>>hiding the pawn loss. Extending a ply partially offsets this... >>>>>> >>>>>>But I have never tested it very thoroughly. I am going to turn it off on >>>>>>one version and play an extended match, 2cpus to 2cpus.. I'll report on the >>>>>>result later.. >>>>> >>>>>I predict the capture extension version will win easily, especially in medium >>>>>blitz games (5 0). I have done that test (but not the wac test), and my program >>>>>definitely plays better with a limited capture extension. >>>> >>>> >>>>I have run 3 100 game matches so far. In the first, the recapture extension >>>>won by a small margin. IN the second, it lost by a big margin. In the third.. >>>>can't report yet... 3 more games to go... >>>> >>>>I am playing fairly fast blitz games which is where I generally see the best >>>>results for extensions... >>>> >>>>More data in a bit... >>> >>>\ >>> >>>300 games... 3 sets of 100 games played at 40 moves in 1 minute, each >>>program getting 2 cpus, ponder=on, etc... >>> >>>match 1. recap wins 26-18 with rest draws. >>>match 2, recap loses 3-20 with rest draws. >>>match 3, recap loses 6-21 with rest draws. >>> >>>games were played with learning=off, without a books.bin/bookc.bin to get a >>>bit of variety... >> >>Don't know what to say about that, except that I will run my test again, games >>to be played on ICC, 5 2, squirtle v squirtx (recap v no_recap). My test >>versions use the same books, but have a random value which selects the opening, >>and also changes the book depth. >> >>Intuitively, and also taking into account the countless articles and many >>programs which adhere to the recapture extension idea, I cannot help but be >>surprised at and question your results. But, as I say, I will report back. >> >>Will > > >No more surprised than I was when I first saw the WAC data either. However, >I have had lots of cases over the years where something worked for someone >else but not me, and vice versa. If you look at main.c in crafty you will >find places where something failed for me at one point, but a year later it >worked fine after extensions or something was changed somewhere else... Ok, I did some testing, and found that my recapture extension doesn't seem to have much effect. I guess I don't understand why that would be the case, but there it is. In most positions, it seems as if you'd be losing a ply if you didn't extend those critical lines. In the WAC test, the recapture version solves 2 more than the non-recap. But in head-to-head play (icc blitz), the recapture version lost 52-56 in a 150 game match. All in all, there appears to be very little difference. I'll probably take it out. Will
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