Author: Robert Hyatt
Date: 17:44:46 01/07/01
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On January 07, 2001 at 16:38:50, martin fierz wrote: >hi, > >i just implemented an MTD(f) search for my checkers program instead of my usual >PVS/NegaScout - it seems to be about same good. in my hashtable i only store the >value and valuetype, and i noticed that in aske plaat's MTD(f) description he >stores both upper and lower bounds in the hashtable. i couldn't figure out a >reason to do this - can somebody enlighten me? i tried in vain to construct some >sequence of null-window calls which MTD(f) might do where it would be of use to >save both bounds, but maybe i'm just missing something simple here?! > >cheers > martin The reason is this: when you search with mtd(f), you bounce around searching a null-window on either side of the _real_ value. When you bounce high, you get a tree where ply=2 moves all fail low. When you bounce low, you get a tree where all ply=2 moves fail high. If you save both bounds, you don't get horribly inefficient when you bounce from below the true score to above the true score, and vice-versa. It prevents overwriting something that might be critical the next search.
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