Author: Tony Werten
Date: 02:06:12 02/12/03
Go up one level in this thread
On February 12, 2003 at 01:06:06, Nathan Thom wrote: >On February 11, 2003 at 20:57:16, Nathan Thom wrote: > >>Ive just finished implementing a Q search for LittleThought, and was trying to >>get a feel for my node stats compared with other engines out there. What % of >>the total nodes searched are Q nodes in varying kinds of positions? eg opening, >>middle game, end game etc. >> >>I have a feeling my q nodes are way way too many :) > >In alot of examples ive seen, an evaluation is done right at the start of the Q >function and if it gives a beta cutoff it returns. I dont understand this. Isnt >the whole point of Q search to prevent scoring unstable positions? If the score >for this position exceeds beta, it may be that it just did QxQ say. That will >give a large eval as one side just lost the Q but the other still has theirs. >But, if the Q search had a chance to continue, it would see that the Q can be >recaptured immediately. > >What gives? You're missing "side to move". If you just did a QxQ then at the start of quiescence it's my turn again. Normally after QxQ my score will not be above beta. You should read the mystical (alpha,beta) as ( my_garanteed_score,your_garanteed_score). If I can get to a position with score>beta, it means I could lower (because of the minus) your (previously) garanteed score. So we can assume you will not play this sequence and therefore we will cut off. Tony
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