Author: Uri Blass
Date: 08:45:56 04/23/01
Go up one level in this thread
On April 23, 2001 at 10:53:50, Ulrich Tuerke wrote: >On April 23, 2001 at 10:43:02, Uri Blass wrote: > >>On April 23, 2001 at 09:45:45, Ulrich Tuerke wrote: >> >>>On April 23, 2001 at 09:34:20, Robert Hyatt wrote: >>> >>>>On April 23, 2001 at 05:52:00, JW de Kort wrote: >>>> >>>>>Dear friends, >>>>> >>>>>I have added a qsearch to my program and as a result the number of nodes in my >>>>>search has exploded. Sometimes the program searches ten times as much nodes in >>>>>the qsearch than in the regular search. Can anybody give me some advice on >>>>>methodes i can use to limit the number of nodes in the qsearch? >>>>> >>>>>Thanks in advance. >>>>> >>>>>Jan Willem >>>> >>>> >>>>A simple idea works well: >>>> >>>>When you enter a q-search node, if the current score is (say) a queen below >>>>alpha, then capturing a pawn or piece is not going to bring the score back up >>>>to alpha. Those captures are useless to examine.. >>> >>>I think that this is just what I had suggested in my reply, but you have >>>explained far better why this should work. >>> >>>You say "useless to examine" . After all, this algo involves some kind of >>>forward pruning and there is a certain risk in missing some tactics. >>> >>>However, I admit that this trick appears to be reasonably safe. I guess, >>>everybody is doing it. >>> >>>Nevertheless I had observed that in some rare cases, a test position will be >>>solved later (i.e. in a higher iteration) as a consequence of this trick. >>> >>>Do you agree ? >> >>I do not understand what is the reason that a test position will be solved at >>later ply. >> >> >>If you search only captures in the qsearch and if the score is more than a queen >>below alpha then one capture that is not a capture of the king is not going to >>change the fact that the score is below alpha. >> >>Common sense tells me that if you capture in the qsearch more than your first >>capture then the line is illogical because it is possible that the opponet could >>avoid the line by not capturing >> >>Example:Searching a line like 1.PxQ PxP 2.PxR is illogical in the qsearch >>because black may save the rook by a different move. > >The sequence of captures may continue for several plys. And may be the whole >sequence brings the material balance back above alpha, whereas the 1st recapture >alone did not. So, in case you cut early there is in principle the possibilty to >miss something. I still do not understand how you can miss something. I assume that the sequence of captures is not sequence of forced moves and the side that captured could avoid capturing. I assume also that you do not search in the qsearch to find if there are quiet moves to avoid captures and the Qsearch includes only captures. In this case the sequence of captures can win more than a queen but the sequence of a capture and after it a quiet move may lead to the end of the captures. Assuming that the sides must capture in the qsearch seems risky to me because you can miss things because of these assumption. It seems to me better to assume that the sides can also avoid moving and prevent the opponent to play captures. Uri
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