Author: Robert Hyatt
Date: 06:41:46 01/30/01
Go up one level in this thread
On January 29, 2001 at 19:10:44, Will Singleton wrote: >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 I played hell testing this, unknowingly. But the data turned out to be useful. I played (I thought) one 100 game match. However, I played 100 games with the winboard match mode option, but I had it in a loop. AFter I found it still running a couple of days later, I looked at the totals and the non-recapture version won by a very significant number. I have disabled it and now require -DRECAPTURE to compile it back in for someone that wants to play with it. I am not sure this is as significant when playing other programs however. As I have said before, playing yourself with 1 minor difference in the two versions tends to exaggerate the difference. However it was (and is) a surprise. One good test case is the kopec suite, position 22, where Bxe4 is the key. With recap I see it at 6, without I see it at 8. But the difference in time is like .5 seconds for 6 vs 3 seconds for 8 (3 seconds due to things being faster without the recap extension). This is a very good example of "test, test, test, rather than taking everybody elses word that it is a good idea. Next suspect is my push passed pawns extension...
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