Author: Robert Hyatt
Date: 06:40:38 01/11/06
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On January 11, 2006 at 02:14:53, Andrew Wagner wrote: >This is going to sound like a really odd question. That's because it is. But I >really do have a good reason for asking it. Anyway, here goes... > >Is it feasible to implemet a typical alpha-beta search in an iterative fashion? >I'm not talking about iterative deepening, but I want to do alphabeta without >any recursion. If it's possible, can you give me a suggestion what it might look >like? Yes, but it simply looks ugly. The idea is that instead of recursive values for alpha/beta/etc, you have arrays alpha[n]/beta[n]/etc. And instead of recursively calling search, you add one to "ply" and go back to the top. Where you access everything as alpha[ply], beta[ply], move_list[ply], etc... The problem after doing that is that you then have to deal with the "negamax" type issue of at each depth, before copying alpha[ply] to alpha[ply-1] (that would be backing up the value) you have to negate the value, so that it is easier to deal with alpha/beta cutoffs. I would not do this unless you are dead set on doing a parallel search this way. My search is recursive, and my parallel search works just fine, keeping the readability of the recursive search. Cray Blitz used the "iterative" type search because when it was initially created in the very late 1960's, FORTRAN didn't support recursion (recursion was hardly used back then, except maybe in Algol/PL-1/etc) so using it wasn't an option... It can be done, but the resulting code is much harder to read, and with everything "global" (thanks to the big arrays) it is quite easy to introduce bugs that are then difficult to find.
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