Author: Vincent Diepeveen
Date: 13:58:01 09/10/02
Go up one level in this thread
On September 10, 2002 at 15:54:09, Dann Corbit wrote: >On September 10, 2002 at 15:48:40, Vincent Diepeveen wrote: > >>On September 10, 2002 at 13:11:02, Dann Corbit wrote: >> >>>On September 10, 2002 at 12:07:37, Vincent Diepeveen wrote: >>>[SNIP] >>>>>(3) Reading Aske Plaat's search & re-search paper, it really seems like mtd(f) >>>>>is something of a magic bullet. But I note it seems that more programs don't >>>>>use it than do (for example Crafty). What is wrong with mtd(f) which Plaat >>>>>doesn't say? >>>> >>>>There is nothing wrong with it. However a softwareprogram must have certain >>>>conditions to let it work well (in hardware other issues play a role) >>>> a) it must be a static evaluation with a small granularity; >>>> if pawn=32 it will work great, if pawn=1000 like in DIEP it won't >>>> work at all, other things aren't interesting then. >>> >>>I have found this to be true also with experiments, and the reason is obvious. >>> >>>The MTD(f) algorithm basically does a binary search between two bounds (on >>>average -- it might be faster or slower in individual cases). If the interval >>>varies from 3276700 to -327600 you have between 22 and 23 searches to resolve >>>it. If the interval varies from 3276 to -3276 you have between 12 and 13 >>>searches to resolve it. >> >>perhaps it is good to clarify one thing. As soon as a MTD search >>needs to use a binary form of search to get from value A to B, then >>mtd will fail of course. >> >>the advantage of mtd is that if you have a bound search at 0.01 which says: >>"it's more than 0.01" then you try 0.02. In this way you need only a >>few minimal windows to get from 0.01 to 0.03 >> >>The statement of Rudolf is very clearly: "such minimal windows are >>very cheap", and looking to SOS i can only agree with him. >> >>A major problem is like bob says if you have a 0.3 difference. >>even with pawn = 100 and 0.3 being 30, that means you need 30 researches. >> >>If you jump binary, then the only advantage which MTD offers is gone directly. >> >>So going from 1000 to 1300 in DIEP that's 300 researches. > >I think even worst case it won't do more than log2(interval) searches. I >suppose it is possible for each search to refine the interval by only 1 unit, >but it seems incredibly improbable. > >I would expect a window of 300 to take about 8 searches to resolve, on average. >Perhaps you tested with some pathological positions? I have not seen behavior >that bad, but maybe I have not looked at the worst cases. The problem is you don't know in advance that it's going to get up 0.300 pawns. And doing a search at 0.001 first then 0.002 that's way cheaper than doing 0.001 first then 0.250. The problem of doing 2 searches of 0.001 and then 0.250 or something, is that this second search is just as expensive as a research of PVS is doing, whereas a search of 0.002 after 0.001 is very cheap. I made myself clear? Best regards, Vincent
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