Author: Bo Persson
Date: 15:07:27 01/17/06
Go up one level in this thread
On January 17, 2006 at 17:55:41, Tommi Rimpiläinen wrote: >On January 17, 2006 at 17:26:59, Dann Corbit wrote: > >>These methods are theoretically unsound, but work well in practice. >> >>A method is said to be unsound if a search to depth K fails to find the best >>move at depth K. Alpha-Beta will not fail to find it. It will find exactly the >>same move as a full minimax search would. >> >>Other sorts of reductions like null move do not provide the same guarantee. >> >>So "technically" they are unsound. But they work very well in practice. >> > >Unless we're dealing with a mate prover, the search results may always be >disputed. That's why, I think, people should not lay too much emphasis on >theoretical soundness. What sould be pursued instead, is that the evaluation >reflects the real value of the root node as propably as possible. But this does >not mean that the unsound techniques should not be justified by some vangue >reasoning. > Yes, part of the "work well in practice" is that a null move search doesn't search to depth K, but to K+1 or K+2. So, even if it is "technically unsound", it still works well, on average. I find it amusing that chess programming is very much about being good "on average", the opposite of real-time programming (where you have to minimize the maximum, to guarantee a response time). As others have pointed out, a level K+2 search without null move is even better, but how do you achive that? :-) Bo Persson
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.