Author: Vincent Diepeveen
Date: 09:44:35 09/03/02
Go up one level in this thread
On September 03, 2002 at 06:12:26, Uri Blass wrote: >On September 03, 2002 at 05:29:37, Omid David wrote: > >>On September 02, 2002 at 20:37:35, Vincent Diepeveen wrote: >> >>>On September 02, 2002 at 13:42:18, Omid David wrote: >>> >>>>On September 02, 2002 at 13:34:16, Robert Hyatt wrote: >>>> >>>>>On September 01, 2002 at 17:08:58, Omid David wrote: >>>>> >>>>>>On September 01, 2002 at 12:08:21, Uri Blass wrote: >>>>>> >>>>>>>On September 01, 2002 at 11:55:32, Vincent Diepeveen wrote: >>>>>>> >>>>>>>>On September 01, 2002 at 10:20:08, Uri Blass wrote: >>>>>>>> >>>>>>>>if you search for aske plaat you will find his stuff on >>>>>>>>mtd online probably. i'm amazed that you don't understand >>>>>>>>that Frans is using nullmove. >>>>>>> >>>>>>>I know that he is using null move but I do not use null move when I search the >>>>>>>line that is in the previous pv because I consider it a waste of time. >>>>>>> >>>>>>>Null move is for prunning illogical lines. >>>>>>> >>>>>>>The pv cannot be illogical line so the only case when I can save nodes by null >>>>>>>move pruning when I am in a pv line is when the position is zugzwang. >>>>>>>In other words I can save nodes only if null move pruning is wrong. >>>>>>> >>>>>>>I understood that MTD says that the pv may be wrong but the first ply of the pv >>>>>>>is always right so it does not make sense to prune after Nc6. >>>>>>> >>>>>>>Uri >>>>>> >>>>>>It depends on what you want; if you want "the first move, only the first move, >>>>>>and nothing but the first move", then use MTD(f). But if you also want the PV >>>>>>(as most of us do), avoid it. >>>>>> >>>>>>The use of null-move pruning follows the logic behind each method: In MTD(f), >>>>>>you only want the first move, so you are free to use null-move pruning even in >>>>>>the PV, something you shouldn't do in regular NegaScout/PVS. >>>>> >>>>>You are not thinking this thru clearly. null-move on the PV makes perfect >>>>>sends. You are searching one ply different. It might suddenly change things >>>>>in a significant way and null-move is the fastest way to dismiss a bad line, >>>>>whether it was part of the PV from the previous iteration or part of some >>>>>non-root move that is hopeless. >>>>> >>>>>You should try it in a program, doing it everywhere and only doing it on non- >>>>>PV searches. I think you will be surprised. I was. The comments in main.c >>>>>should explain when I made this change myself after someone (Bruce I think) >>>>>suggested it and testing proved him correct. >>>>> >>>>> >>>>> >>>>>> >>>>>>P.S. >>>>>>Aske Plaat first introduced MTD(f) in his 1995 article "An Algorithm Faster than >>>>>>NegaScout and SSS* in Practice" available at >>>>>>http://www.cs.vu.nl/~aske/Papers/hk.pdf >>>>>> >>>>>>For a more intuitive explanation, look up http://www.cs.vu.nl/~aske/mtdf.html >>>>>> >>>>>>Plaat suggests that MTD(f) is faster than NegaScout, but he researched only >>>>>>fixed-depth full-width trees. I haven't seen any publication concerning MTD(f)'s >>>>>>behavior in variable depth trees (e.g. using null-move pruning). >>>>> >>>>> >>>>>I suspect it is "break even" once you get it right. NO way to avoid at least >>>>>two searches, and, in general, more than that. Which means that with a program >>>>>with a complex evaluation, the researches are going to cause problems and make >>>>>it catch up to PVS or even pass it. >>>>> >>>>>I think that for normal programs, they should be equivalent if they are both >>>>>implemented with the same skill and development time. >>>> >>>>Actually I think MTD(f) needs more time for fine tuning. For example, you have >>>>to adjust the evaluation function to a good degree, since the behavior of MTD(f) >>>>can change to a great extent depending on the eval function; while PVS isn't >>>>that dependant on the eval function. >>> >>>It is the opposite. MTD works for idiotic random tree searches (especially >>>not having a qsearch like in aske's experiments that's the case). >> >>This confused me for some time: didn't Aske use at least qsearch? He speaks of >>fixed-depth full-width trees, but even there (in such a brute-force framework) >>lack of qsearch doesn't make sense. What's the point if I capture your piece and >>don't see the recapture in the next ply... >> >> >>>Also >>>for programs who are very bad in ordering moves and have huge overhead >>>otherwise to determine a good PV (which i get with PVS directly out of >>>hashtable already, like if score drops it doesn't take that much >>>time here for example, where others take ages when score drop which >>>i explain by a program that needs too much overhead). If you have pawn = 32 >>>then MTD works great of course. >>> >>>If you have pawn = 1 it works EVEN better. >>> >>>the more silly your evaluation the better. of course major bugs which cause >>>big deviations in evaluation are not very good. >>> >>>However fritz is well tuned. >>> >>>But by far best working is just returning material >>> pawn=1 >>> knight=bishop=3 >>> rook=5 >>> queen=10 >>> >>>try it with these piece values. then compare all algorithms. you'll see, >>>MTD will outperform *anything* with simple evaluations. >> >>With simple evaluations (material only) I think you are right. Such experiments >>will be closer to Aske's ones. >> >>Once I worked for some time on the MTD(f); my major problem was the odd/even >>problem of the evaluation function. Although using the value of two plies ago >>(instead of last ply) minimized this problem, I still got better results with >>the PVS. Well, but maybe I didn't spend enough time on that... > >I prefer not to work about something that can cause me to lose information and >it is not clear if it is better. > >Not having correct pv is losing information. > >Even if Vincent is right and MTD(f) is good for Movei of today because of it's >simple evaluation I still prefer not to try it because I expect my evaluation to >be changed in the future and I do not like the idea of working on something only >to undo it later. > >Uri I do not know how you program, but switching diep from PVS to MTD used to be a single flag. I'm not lazy evalling nor forward pruning, so there didn't change much in qsearch either for me. Sincethen i ignored the #define and i wold need another few minutes of modifications to test again with MTD. It's real simple. We talk about a couple of tens of lines only.
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.