Author: Dr. Axel Steinhage
Date: 01:38:04 01/27/05
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On January 26, 2005 at 12:59:42, Robert Hyatt wrote: >On January 26, 2005 at 08:50:03, Dr. Axel Steinhage wrote: >Your case of "fail high" seems to be terribly expensive. Doubling the size of >the tree at a minimum, because to search the second move after you have a >fail-high is pure overhead. DB did this as well, but they did do a search to a >significantly reduced depth, rather than a normal search. Hsu called this "FH >singular" (fail-high singular). I implemented it exactly as he spelled it out, Thanks for your comments! Just wanted to comment on this reply from you (above): My "fail high" is not expensife, because I also go on searching with reduced depth (I think I wrote that I use a reduction factor of R=2). Maybe I did not make myself clear enough. I think the main difference between my algorithm and the others I have seen so far is, that I NEVER touch a move twice and I don't even have to generate all moves most of the time. What Hsu et Al did was to FIRST find the best move and THEN test whether it is singular. What most people do today is FIRST do a complete search (although at reduced depth) to find a singular move and then search the whole branch again with the singular move having higher depth, right? This also means to touch this branch twice. What I do, however, is only to GO ON searching (with reduced depth!) after a fail high. So no RESEARCH but a CONTINUATION of the search. This seems costly, but it may not be! Most of the time the next move I search (after the fail high) is already within the Singular window (or a fail high again). Plus, I have many conditions where I don't have to go on searching anyway. It seems that the test for singularity produces nearly no overhead. Only the actual extension. But as you stated: this may already be too much overhead. I can believe, that SE is somehow orthogonal to Nullmove. I will go on testing. I did not do complete testing so far. I only checked the solution times for a set of test positions. But that does not mean anything for the practical game later on. I will keep you up to date on my findings, if you like. Thanks, Axel
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