Author: Vincent Diepeveen
Date: 06:50:26 06/22/99
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On June 21, 1999 at 14:34:20, José de Jesús García Ruvalcaba wrote: >On June 21, 1999 at 13:53:48, James Robertson wrote: > >>My program does check, recapture, and pawn push extensions, but I have heard >>that many programs do a lot more. I think Gromit said he does something like 10 >>different extensions? >> >>Could someone please tell me what different kinds of extensions are sometimes >>used? It would be cool to try them out on my program. >> >>James > >1. Pawn ending extension. Extension invented by Walter Ravenek. i'm already searching like 40 ply in any pawn ending, but the thought is obvious; if you exchange TO a pawn ending then every move gets extended. you see quickly when you can exchange to a pawn ending then. a lot of programmers are nowadays doing it. >2. Fail high extension. how can you call that an extension! >3. Preferred variation extension. that's crap. >4. One-reply extension. >5. Singular extension. >6. Enabled move extension. enabled move extension that asks for more explanation! > I have an idea; but I have not tried it as I am not a chess programmer. Extend >on moves which drastically (this has to be defined) increase the mobility and/or >decrease opponent's mobility. Moves which do the opposite can be forward-pruned, >too. What is written above is crap. To describe most common extensions; - check extension always, or limit it. Why extend every check like e4,e5 Qh5,Nc6 Qxf7?? - threat extension; if nullmove returns threat then extend. don't extend all times nullmove returns threat. most common is to extend when nullmove returns mate score. I call that mate threat extension. I limit this a lot, yet this extension still works great. - recapture extensions; this never brought me anything, yet most programs are doing it. i guess it's depending upon what you try in qsearch. the more accurate your qsearch is the less you need of these is my thought. i don't do them - singular extensions; i've tried this thousands of times, but never found them working. A singular extension is in fact a case of threat extension; there is a threat that only allows a single move to prevent it by a margin S. Threat extension doesn't have problems with S, and also extends when more than 1 move prevents the threat. - passed pawn push extensions; i'm doing a few of those. can blow up your search awful sometimes i limit it considerable. - one reply extension; when you only have 1 legal move, then extend it independant from other extensions you already have in that pos (like check) - check evasion; after giving a lot of checks, it might be worth giving some more checks (as a kind of selective search to find a checking sequence that might mate). - high score extension. To prevent horizon effects to occur, one can extend if a certain pattern is on the board which gives a high score in evaluation. For example: if a queen is attacked, and you give a high score for a queen being attacked, then you might want to extend it, resulting in a better leaf score. Of course this extension needs to be done near leafs and not in the middle of the search.
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