Author: Robert Hyatt
Date: 14:30:08 02/29/00
Go up one level in this thread
On February 29, 2000 at 11:06:45, Sanjiv Karnataki wrote: >On February 29, 2000 at 08:39:14, Robert Hyatt wrote: > >>On February 29, 2000 at 03:19:00, Bas Hamstra wrote: >> >>>On February 29, 2000 at 01:34:48, Sanjiv Karnataki wrote: >>> >>>>Hi All, >>>> >>>>I just finished reading Ernest Heinz's article on the subject and I had a >>>>question about the code sample. It uses a routine called "try_null" that is not >>>>given in the article and the only thing the article says is "tries to avoid >>>>superfluous null-move searches that do not really promise to cut off as decided >>>>by the function try_null" >>>> >>>>Does anyone know how that decision could be made? I was thinking of trying it in >>>>my program. >>>> >>>>Thank you >>>> >>>>Sanjiv. >>> >>>For instance if material is more than PawnValue below Alpha,chances are there >>>will be no cutoff. Not perferct of course. >> >> >>Also the hash table trick (used in crafty and many other null-move programs) >>can be used. If you get a hit on the hash table, but the depth is not deep >>enough to let you take the true score of cutoff score, it still might be good >>enough to prove that a null-move search won't fail high (see search.c in Crafty >>source, look for "avoid_null". Then look at hash.c to see how this gets set to >>disable a null move at this position.) > >I had a question about that: > >Crafty also hashes the threat flag if the null move failed low to mate-in-N. Why >does it not use that in hash.c also to avoid null move? > >Thank you. > >Sanjiv. threat should be set already... 'threat' means this leads to getting mated if you 'pass'. If that is set, null-move shouldn't be done. But if that is set, this node can't fail high from the hash table either, so it still won't be done...
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