Author: Bruce Moreland
Date: 01:23:09 08/11/99
Go up one level in this thread
On August 11, 1999 at 03:11:25, Shep 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? :) > >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... :-] It is extremely unlikely that anyone would intentionally do this, I believe. It would be more complex than you think, it would be a possible source of bugs, and it would serve almost no purpose. bruce
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.