Author: Tord Romstad
Date: 08:39:13 11/03/03
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On November 03, 2003 at 10:20:36, José Carlos wrote: >On November 03, 2003 at 10:08:08, Uri Blass wrote: > >>I also explained later in another post why I think that null move pruning can >>reduce the % of first fail high without changing the function of order of moves. > > > I've changed the subject because I want to speak about this now, which is very >interesting for me. > I missed your previous post when you talked about null move and move ordering, >and I'll search for it in the search engine. > I'm having a hard time trying to make null move work together with a high % of >beta cutoffs at the first move. Unlike you, I find this statistic very useful >because I can try several tricks to avoid non-productive null move searchs which >will damage move ordering. Why do you thing it damages your move ordering when the null move search does not fail high (I assume that is what you mean with "non-productive null move search")? I have found precisely the opposite to be the case. When the null move does not give a cutoff, it usually gives a nice killer move to try at the next ply. > So far I'm being able to average >95% in games, hitting some times 99%, at the >cost of not pruning some lines. Is this the percentage of null move searches which fail high? If the answer is yes, >95% looks rather good. I think I had less than 90% the last time I checked. I have difficulties finding good rules for when to avoid the null move search. Currently I avoid the null move if the evaluation function has detected a mate threat, a hanging queen or some other major threat, or if the static eval returns a value much worse (from the point of view of the side to move) than the root score from the previous iteration. I don't like the common trick of avoiding the null move search when the static eval is below alpha, because it gives too many search inconsistensies. >I'm not sure so far about where is the correct >balance between both pruning and move ordering, but I'll report my results when >I think they're significant. > On the other side, I haven't found other pruning different than null move to >affect move ordering, though I must admit I'm very conservative at the moment. > Also a complex qsearch helps move ordering but damages branching factor. I am not sure what your definition of a "complex qsearch" is, but removing checks from my qsearch does not seem to have any effect on the branching factor for me. Tord
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