Author: Robert Hyatt
Date: 20:58:10 02/13/03
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On February 13, 2003 at 15:23:15, Peter McKenzie wrote: >Just wondering how many programs are using the Enhanced Tranposition Cutoffs >algorithm, or if people have tried it and had trouble with it. I think I'll >have a go at implementing it shortly. I tried it several years ago with no success. IE the cost was a wash with the reduced tree size, but that was all. I had to write a special "Make()" function that did nothing but update the hash signature so that I could probe to see if the new position would produce a quick cutoff. Since there was no gain (and no loss) I stopped using it. YMMV of course, and checker programs seem to report good results using this, but their tree is a different shape. > >For those interested, here is the basic idea: > >When searching a position, the first thing done is a search of the hash table. >Assuming this doesn't result in a fail high, we then try ETC. > >For each possible move, do a make move and check the hash table. If the hash >table indicates that the side to move would fail low (it must have sufficient >draft of course) then you can fail high in the original position. > >I guess the tricky thing is making sure that alpha and beta are handled >correctly. > >There are possible tricks to make it work better: >- only do ETC when remaining depth is reasonably high >- have a special fast makemove which updates the hash key only >- even if ETC doesn't provide a cutoff, perhaps it can help move ordering > >Any tips are most welcome. > >thats all, >Peter
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