Author: Robert Hyatt
Date: 07:34:30 09/19/04
Go up one level in this thread
On September 19, 2004 at 03:21:41, Richard Pijl wrote: >On September 18, 2004 at 23:57:32, Robert Hyatt wrote: > >>On September 18, 2004 at 18:50:22, Richard Pijl wrote: >> >>>On September 18, 2004 at 11:28:45, Sune Fischer wrote: >>> >>>>On September 18, 2004 at 11:09:26, Robert Hyatt wrote: >>>> >>>>>On September 18, 2004 at 04:05:38, Sune Fischer wrote: >>>>> >>>>>> >>>>>>I decided to try out the triangular PV thing Bob >>>>>>speaks so highly of, to see if it improves move ordering... >>>>>> >>>>>>I was careful to terminate the PV on all exact scores - of course. >>>>>>Still I was getting illegal moves in the PV. >>>>>> >>>>>>It turned out to be a hash/nullmove problem. >>>>>> >>>>>>See, in the hash I adjust the window down on UPPER bounds, ie. >>>>>>something like: >>>>>> if (flag==UPPER && score<beta) >>>>>> beta = score; >>>>> >>>>>Are you doing PVS? If so you won't do this a dozen times during a long search, >>>>>most likely. But I do this in Crafty as well, and it doesn't _ever_ get illegal >>>>>moves in the PV. >>>> >>>>I haven't looked but I guess you are doing something equivalent to what Richard >>>>suggested with beta = score+1. >>>> >>> >>>It may be less important when doing fail-hard. Chances that the upperbound >>>equals the real score is lower with fail-hard. >>>Richard. >>> >> >>I'm not sure why it would matter. You should fail high, relax the upper bound, >>and get the _same_ value back except this time it will be an exact score... >>That is pretty normal to get a fail high and then on the re-search, getting the >>same score again since the upper bound and true score were identical... > >Are you doing a research on a fail high in an innernode (when the beta was >adjusted)? If you do, you're right. It won't matter. >What I meant was, that with fail soft chances are bigger that a stored >upperbound equals the true score as it can return a score outside the ab window. Again, I can't see how that would hurt. If I get a score outside the root AB window, and it gets backed up to the root, I have to re-search with a wider window, which will catch those "edge" conditions. > >>This doesn't cause oddball PVs in Crafty however, even though I see it on >>occasion... (see the identical score/upperbound problem, but no illegal moves >>in my PV ever). Nor did it ever happen when I used true fail-soft years back... > >I don't think adjusting bounds will cause anomalies in the PV other than perhaps >short pv's (when doing beta=score and no research) as the fail high will >truncate the pv. A fail high can't possibly terminate the PV in a correct search. You can't have a PV that ends on a fail high, as it is illegal, except for mtd(f) searches which I assume we are not talking about,. >Richard.
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