Author: blass uri
Date: 22:53:35 08/10/99
Go up one level in this thread
On August 11, 1999 at 00:24:08, Robert Hyatt wrote: >On August 10, 1999 at 22:03:27, Andrew Dados wrote: > >>On August 10, 1999 at 21:35:12, Robert Hyatt wrote: >> >>>On August 10, 1999 at 19:56:10, Marc Plum wrote: >>> >>>>A while back I ran some multiple engine tournaments within the Nimzo99 >>>>interface. One thing that I noticed was that some programs would make >>>>meaningless underpromotions. That is, in a position where a promoted pawn would >>>>be immediately exchanged anyway, the computer might promote to a bishop or rook >>>>rather than a queen. I had occasionally encountered the same thing in my own >>>>games with computers; I also found a small number of computer games like this >>>>when doing a database search for underpromotions. I don't have any statistics >>>>to present; I'm just noting that this happens not infrequently. >>>> >>>>When a human player does this, he is probably just being whimsical, or it could >>>>be a psychological ploy. I wonder, though, why a computer would do it. Is it >>>>just a random thing? Does the computer reason that losing a bishop is less bad >>>>than losing a queen, even though the resulting position is the same? Or do >>>>computers like messing with people's minds too? >>>> >>>>Marc Plum >>> >>>Actually at times there is a valid reason. If (say) d8=Q is a check, and d8=R >>>is not, then the program can choose whichever one maximizes the evaluation. How >>>could they be different? Remember that one is a check and will extend the >>>search while the other is not. So if searching one extra ply discovers >>>something interesting, then =Q will get played. If searching one extra ply >>>discovers something bad, then we avoid seeing the 'bad' by playing =R. >>> >>>Cute, eh? :) >> >> However there are cases when underpromotions are *totally* meaningless and >>still made by some programs. While hashtable should prevent re-searching >>a8=N Bxa8 because there should be score for a8=Q Bxa8, it looks like either hash >>entry can get overwritten or some programs don't calculate exact same signatures >>in those 2 lines. Or else? (Note that hashtable hit returns 'true' score, >>because a8=Q was searched full-width to become PV. It can be that some programs >>don't store 'true score' in hash so researching with 'new' bounds may produce >>new score). >> >>-Andrew- > > >Don't forget the 'check'. If you try a non-checking promotion first, and put >the entry in the hash table, then search the checking move, the hash entry will >be useless, because it will be one ply 'short' of the depth required since the >check incs the depth. What is the problem to tell your program to search the promotion to queen before searching underpromotions and to tell it that if the right move against promotion to queen is taking the queen then not to analyze underpromotions? Uri
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