Author: Dave Gomboc
Date: 08:41:58 06/14/99
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On June 14, 1999 at 09:30:07, William Bryant wrote: >On June 13, 1999 at 21:10:57, Pat King wrote: > >>Before implementing null move, I had a simple aspirated AB search, and would >>research with a window of (Beta, Infinity) for fail highs and (-Inifinity Alpha) >>for fail lows. And life was good. With null move, however, it's not uncommon for >>my program to get stuck, alternately failing high and low, without ever properly >>resolving the score. What's up with that? Must the research be done >>(-Infinity Infinity)? Or is this a sign that I've a bug in the null move code? > >Pat, > > I just struggled with the same think, and I agree with Will that this should >be part of a FAQ. It was explained as follows, when switching from a alpha-beta >window to a beta-Infinity window, the search allows other possibilities that now >return a fail low score. It happens. I track it and I get a fail low following >a fail high about every 100 test positions or so. I can send you some positions >that seem to cause this. > > Now for practical advice gleaned from this group. Beleive the initial fail >high. If I fail low after a fail high, I ignore the fail low -- keep the fail >high. Therefore the move that failed high should become the new PV move >although you don't have a continuation and an exact score. I have seen the opposite advice as well (ignore the initial fail-high). I don't think a definitive solution has been recognized. Dave
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