Author: José Carlos
Date: 16:50:15 08/08/04
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On August 08, 2004 at 04:35:54, Tord Romstad wrote: >On August 08, 2004 at 01:47:12, Stuart Cracraft wrote: > >>Now my new question is what features do you think would help in solving >>problems rapidly. Extensions? > >Yes. But be careful -- It is easy to introduce lots of extensions which makes >your engine very good at solving problems, but which greatly reduce the >playing strength in real games. You should always play some test matches >before you decide whether you want to keep some new extension in your >program. > >The most useful extensions for solving problems rapidly are: > >1. Checks. > >2. Single reply to checks. > >3. Mate threats. These can be detected statically, or by using the return >value of a null move search. Extend if the null move search returns >-MATE_VALUE+Ply+2. > >4. Attacking moves. If you evaluate all internal nodes (as I do), compare >the value of the king safety component of the evaluation function before >and after a move is made. If a move dramatically reduces the opponent's >king safety, you extend. Another idea that seems to work for me (in my non-released private engine, where I evaluate internal nodes) is to consider the king safety changes along the path. A single move is not likely to make a big change (unless some crazy sacrifices in king's pawn shelter), but some manoeuvres do the trick. I don't recall the details, but the idea goes like this: if (eval[ply] > eval[ply-1] + MARGIN1) extend; if (eval[ply] > eval[ply-2] + MARGIN2) extend; if (eval[ply] > eval[ply-3] + MARGIN3) extend; Where MARGIN3 > MARGIN2 > MARGIN 1, and eval means king safety evaluation of the opponent. Or maybe I used full moves (ply-1,ply-3,ply-5), I'm not sure. It's been a long time without doing chess programming. But the idea worked very well in tests, and made the engine play interesting games also. José C. >In order to avoid search explosions, you may want to use fractional >extensions. I extend by a full ply only for checks. > >Tord
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