Author: Richard Pijl
Date: 08:26:28 12/20/02
Go up one level in this thread
On December 20, 2002 at 10:54:01, Vincent Diepeveen wrote: >On December 20, 2002 at 08:23:59, Russell Reagan wrote: > >No futility is 100% different from lazy evaluation. > >Futility in fact selects less moves (in qsearch) >based upon alfa or beta and lazy evaluation gives >back a quick score a lot of the times. They are still related in a sense that both 'cut-off' the work to be done by saying that it can't get good enough to improve alpha, so better stop working on it. > >If you search a ply deeper a futile pruned move should not >get pruned, whereas a lazy evaluated position will give problems >no matter what depth you search. > >In contradiction to draughts where everything is seen fullwidth, >in computerchess the effect of futility can be very bad too, >because last 3 to 4 plies (R=2 versus R=3) the qsearch is returning >back a score instead of a full search. > >If that misses major problems then you are in trouble. > >The argumentation of Heinz that futility is correct, is using the >assumption that an evaluation doesn't get a big score for positional >matters. The problem is that todays top programs do give big scores >though. Although Baron is not a top program yet I'm starting to feel this. To be sure that the wrong nodes aren't getting pruned I wrote a little piece of test code. It returned the highest difference it found between the lazyeval score and the full eval score (but not with passers on the board, and not in the endgame). I added 20% to this and that was the threshold used for both lazyeval and futility pruning. It turned out that with every release of the Baron this value increased. Now I'm working on 0.99.4 and the margin was getting very large, more than 5 pawns. After a little test what futility pruning and lazy eval were giving me I decided that it was just too little to risk the problems above. From 0.99.4 (beta 3) on lazyeval and futility pruning (including extended fut.pruning and lim. razoring as described by Heinz) are no longer used. Instead I increased the number of search extensions I have. The result of this: Searching 1 ply less, but searching deeper ... Richard.
This page took 0.01 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.