Computer Chess Club Archives




Subject: Re: Unexpected problem with futility pruning ?

Author: Tord Romstad

Date: 15:16:39 12/29/03

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On December 29, 2003 at 16:01:08, Andrew Williams wrote:
>I make sure that I have a legal move available before pruning stuff.

This is good advice, and reminds me of an amusing bug I had in early versions of
(while I was still using normal futility pruning):  In positions which were so
bad that all
moves were pruned because they had no chance of bringing the score anywhere
to alpha, the engine thought:  "I have no moves, but I'm not in check -- It's
Let's return 0".  As a result, the engine would sometimes make horrible
blunders, and
print out PVs where it sacrificed almost all its pieces, with a draw score at
the end of
the line.


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