Author: Omid David
Date: 10:42:18 09/02/02
Go up one level in this thread
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.
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