Author: Robert Hyatt
Date: 10:34:16 09/02/02
Go up one level in this thread
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.
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.