Author: Robert Hyatt
Date: 19:42:56 10/21/03
Go up one level in this thread
On October 21, 2003 at 16:31:11, Tord Romstad wrote: >On October 21, 2003 at 14:43:45, Robert Hyatt wrote: > >>On October 21, 2003 at 11:53:02, Tord Romstad wrote: >> >>>I don't run my engine through WAC very often, but before releasing a new >>>version (which I will do within a couple of days) I run the whole suite as >>>a sanity test. This time, the following position made me worried: >>> >>>[D]8/8/2Kp4/3P1B2/2P2k2/5p2/8/8 w - - bm Bc8; id "WAC146"; >>> >>>Previously, my program had no problems with this position. The new >>>version, which is the first one to include tablebase support, prefers >>>Bd3 instead of Bc8. At ply 21, the score is +12 for white. When I >>>disable tablebases, the program plays Bc8. >>> >>>Does Bd3 also win, or should I look for yet another bug? >> >>Bd3 is a second solution. It has been in my version of the test since >>I first found this myself, years ago. > >I'm relieved to hear that. I will add this solution to my EPD file. > >>>One of the hardest positions in WAC for my engine is number 163: >>> >>>[D]5rk1/2p4p/2p4r/3P4/4p1b1/1Q2NqPp/PP3P1K/R4R2 b - - bm Qg2+; id "WAC163"; >>> >>>On a Pentium IV 2.4 GHz, I need 11 plies and 1m53s to find the winning move. >>>The problem is to find the line 1... Qg2+ 2. Nxg2 hxg2+ 3. Kxg2 Bf3+ 4. Qxf3 >>>exf3+ 5. Kg1 Rf5! followed by Rfh5. Without nullmove pruning, this position >>>is solved within a few seconds. >>> >>>This is rather annoying, as I have lost more games than I would like on >>>the ICC because of missing similar tactics. Are there any inexpensive >>>tricks to help me solve this kind of positions more quickly? >> >> >>I pick this up at depth=9, time = 2 seconds (using one cpu on my dual 2.8 >>xeon box). All I can guess is that I do extensions a bit differently, >>somehow, or the adaptive null-move R=3~2 idea helps a bit. > >I tried changing from R=3 to R=2, and that just resulted in an even slower >solution. >However, I found that searching checks in qsearch in the endgame (normally I >only do this in the middle game) helps. With checks in qsearch enabled in the >endgame, I need 8 plies and 2 seconds. I'm afraid this will slow me down >too much in other endgame positions, though. > >I'll probably have to play around a bit with my extensions and see if I can find >some other way to find Qg2+ reasonably quickly. > >Thanks for your answer, and thanks to Uri for all the data for other engines! > >Tord Note that my q-search has no checks whatsoever, also...
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