Author: Robert Hyatt
Date: 18:35:12 08/10/99
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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? :)
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