Author: Shep
Date: 00:11:25 08/11/99
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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? :) There might be yet another very clever reason: If program A sees the promotion, his opponent, program B, will see it too. So Program B expects, say, d8=Q and has this information in its permanent brain. But Program A sees the promoted pawn will be immediately captured. So what would you do here if you were program A? Since it is meaningless whether you promote to Rook or Queen, what would you promote to? A queen, which Program B expects and which will allow it to use its PB info? Or a Rook, which takes Program B out of its PB and force it to re-search the position?? See my point? I suppose it would be very easy to add such a promotion rule to a program, right, Bob? :-) [I have seen programs which just about always promote to a rook if they see an immediate recapture (IIRC, MChess and Hiarcs are some of them). This is more than a conincidence... :-] --- Shep
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