Author: Robert Hyatt
Date: 19:05:56 10/14/98
Go up one level in this thread
On October 14, 1998 at 21:13:07, Roberto Waldteufel wrote: > >On October 14, 1998 at 12:45:08, Robert Hyatt wrote: > >>On October 14, 1998 at 12:18:37, John Coffey wrote: >> >>>On October 13, 1998 at 20:37:43, Robert Hyatt wrote: >>> >>>>On October 13, 1998 at 18:41:22, Mark Young wrote: >>>> >>>>>On October 13, 1998 at 17:35:34, Robert Hyatt wrote: >>>>> >>>>>> >>>>>>After reading this thread, I decided to run a test myself. I started >>>>>>off with 20 games of crafty vs crafty, white having KQ and no tablebases, >>>>>>black having tablebases. At 20 seconds per move, this ended in 20 wins >>>>>>for white which surprised me. I took several different positions (20 in >>>>>>total) most of which were mate in 30 or greater and gave crafty 20 secs/move >>>>>>using 1 cpu on my ALR. All wins. I didn't expect this. >>>>>> >>>>>>I then repeated this at 10 secs/move. All wins. >>>>>> >>>>>>I then repeated it at 5 secs/move. All wins. I was going to try 1 sec >>>>>>but decided that to the computer, this is far easier than I thought. It >>>>>>seems that the simple heuristic drive king to the edge, then to the >>>>>>corner, is enough. It didn't play it perfectly, but it never slipped more >>>>>>than 2 moves from optimal at any single move. And when it started off at >>>>>>mate in 34, the "game" never went past 40 moves. >>>>>> >>>>>>So, I retract my original feeling, that KQ vs KR is hard with the KR >>>>>>side having a database. It seems it is a "trivial" ending regardless of >>>>>>having them or not. >>>>>> >>>>>>Most surprising... >>>>> >>>>>It happens to the best of us. I wonder if this simple idea of driving the king >>>>>to the edge, then to the corner is what the Grandmaster's caught onto so quickly >>>>>after only drawing the first few times, or did they find some other idea that >>>>>also works. >>>> >>>> >>>>No.. there's more to it than that... the main problem is the rook on the >>>>opposite board, checking the king at the right time, also preventing the >>>>king and queen from getting on the same rank or file for a skewer... and >>>>the check lets the king "out" to the other side where it has to be done >>>>again, and once it it out, the 50 move counter usually ends the game. >>>> >>>>I am utterly amazed that a 5 second search can solve this. Had you told >>>>me this a year ago I'd have laughed. As it was I was skeptical. And when >>>>I saw it I was *still* skeptical and was looking for a setup error in my >>>>experiment. >>>> >>>>I still want to try at 1 sec / move however... >>>> >>>>but this is definitely easier than KBN K now... to the computer, because >>>>it takes a special piece/square table to win, since you have to drive to >>>>the right corner as well... >>> >>>Although i doubt that any program can see the solution all the way through in >>>such short time, I am sure that they can find a position that >>>brings them closer to a solution (such as getting the king to the side of the >>>board or corner, as you have said.) >>> >>>John Coffey >> >> >>this is the point... a few moves by crafty (non-tablebase) looked pointless and >>I would peek at the other program's log file only to discover the mate distance >>went down by 1. After studying a minute or two, the pointless move covered a >>square so that the "great flying rook" couldn't check from the rear and let >>the king out of the box. >> >>Another thing that is interesting is that it is really not difficult to play >>this ending perfectly. One thing I noticed, in studying the games, is that at >>any given position, there are always a couple of bummers that let the king back >>out to the center and start things over. But there are also *lots* of moves >>that are either optimal or within 1 of optimal. Which means that this is a >>pain for people, to avoid missing those 1/2 moves that break the king back >>out, while for a computer, only interested in squeezing the king to the corner >>with no idea it can be mated, these odd moves are obvious and are avoided with >>ease. >> >>I just would never have believed this is easier than KBN vs K for a computer. >>KBN can be a problem in worst-case positions, because a very short search >>doesn't shed much light on forcing the opponent to the edge... you have to first >>get yourself off the edge and into the center, so it takes a weak centralization >>score for the winning side, and a stronger de-centralization score for the >>losing side, to make this ending happen without tablebases and using a very >>shallow search... > >I use this technique for mating a lone king with major pieces or pair of bishops >(except I now use self generated tablebase for straight KQK or KRK with no other >pieces), but surely for KBNK you need two evaluations, depending on the bishop >you have, since the king needs to be forced into the right corner. This could >easily be handled by a preprocessor, and would be well suited to piece-square >value tables. There are also a small number of positions in KBNK which are drawn >even with the stronger side to move, due to the knight being trapped, which can >never happen in KQK, KRK or KBBK mates, so the evaluation function becomes more >complex if this is to be taken into account as well. Has anyone succesfully done >KBNK with an evaluation like this and a shallow search? My attempts were not >terribly encouraging. Of all the lone king mates, I think KBNK is the one best >suited to solution by tablebase, since the search and evaluation based on >centrality works so well for the others. > >Best wishes, >Roberto the last time I tried this, on a P5/133, crafty at 1 minute per move could beat a tablebase program from the worst case (mate in 34) within 50 moves. When I tried it at real fast time controls, it could win, from this position, but not within 50 moves. For more normal positions, which are mate-in-15 or so, it could win those quite easily... It only needs enough search to see the mate at the end, something like a mate in 4 or so, which takes a fraction of a second. I have two "mate boards" and use the "right" one depending on the bishop I have. I assume it still works, but will run the test in a few minutes on my notebook to see... just like KQ vs KR tests...
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