Author: scott farrell
Date: 09:52:59 01/17/03
Go up one level in this thread
On January 17, 2003 at 01:20:23, Omid David Tabibi wrote: >On January 17, 2003 at 00:48:48, Robert Hyatt wrote: > >>On January 16, 2003 at 20:29:54, Omid David Tabibi wrote: >> >>>[D] 4k3/8/8/p1p1p1p1/PpPpPpPp/1P1P1P1P/8/4K3 w - - 0 1 >>> >>>At the above position, some programs (e.g. Fritz, Hiarcs, Crafty) reach their >>>maximum depth in a second or two (see the Crafty analysis below), while others >>>(e.g. Tiger, Shredder) need more time as they search deeper (Tiger for example >>>quickly reaches depth 20, and then slowly goes deeper and deeper, see the Tiger >>>analysis below. For Genesis it takes about 4 minutes to reach depth 60). What is >>>different in the former class which enables them to quickly reach the max depth? >>> >> >>This is a hashing problem. There are not many unique positions, so hashing >>should cause the search to be very efficient... nothing but king moves helps >>this even more. >> > >There are only 16 (white) x 24 (black) x 2 (sides) = 768 unique positions. But >still normally you cannot retrieve everything from hash table: Let's say you >have a position stored in hash table with depth 30, but now you need a depth 31 >search, so you cannot use the hash result; after the next iteration you will >need a result for depth 32 and so on and so on... > >Genesis gets about 30% hash hits from the above position. > > >> >>>Another interesting point is that Crafty (and many others) gradually reduce the >>>score as they searches deeper (in the below log you can see that at depth 47 >>>Crafty gives the score 0), while some others like Tiger, remain with their fixed >>>score (-0.24 in the log below). Based on what factors is the score reduced in >>>Crafty? >>> >> >>Probably draw by repetition. The side that is behind won't move his king very >>far from the original square. The other side will try every possible square >>but after 40+ plies he runs out of new squares and the other side can force a >>repetition. > >If so, then why doesn't that happen with all the engines? Tiger never changes >the score; Genesis reached the depth 80 and never changed the score (and to the >best of my knowledge Genesis doesn't have any repetition detection bugs). >Besides, the score drop is usually gradual, not a sudden change to 0. My chompster engine has some experimental blockade detection, the score starts around0.05 and gets to 0.0 by ply 8 with about 2000 nodes. And depth20 has only 20000 nodse, and a score of 0.0 still. I am thinking other commerical might have bloackade detection, and if they did, they would behave markedly different to those that did not. Scott
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