Author: David Rasmussen
Date: 08:57:49 12/08/00
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On December 08, 2000 at 06:18:45, Vincent Diepeveen wrote: >On December 07, 2000 at 13:56:31, Bert van den Akker wrote: > >>In a previous question about Futility pruning Vincent Diepeveen mentioned: >> >>>Futility pruning is very dubious. It sure speeds you up, but it's >>>dubious and tends to give you slight positional >>>differences that make a program play positional >>>a lot weaker. >> >>Can sombody explain me why Futility pruning tends to give slight positional >>differences? > >First of all it heavily relies on the positional evaluation of >a program. If you have a very simple evaluation with small scores >then the problem is a lot smaller when you have huge scores (no matter >the size of the evaluation). > >Suppose i am in a position X where evaluation of the position is > > 0.055 > >Now suppose alfa is 0.500 > >Suppose i use a value 0.400 to create a region but that >a move i delivers after making a move an evaluation of 0.700: > > So for move i the rule: > if( eval(X)-region <= alfa ) > prune move i > >Obviously this way of pruning is HEAVILY dependant upon what >a move positional can deliver to me. Is it a huge score, then >you have a major problem because the smaller the value 'region' >in the above example the more one can prune. The bigger i make >the value 'region' the less one can prune. > >Not to mention that a move can place down a tactical trick, like >threatening mate, and as i do checks in the qsearch, >i see the completion of it in the qsearch. > But this wont happen if your margin is large enough. As large as your largest position scores. As explained by Ernst. Very simple. And accurate.
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