Author: Dann Corbit
Date: 17:11:53 01/14/04
Go up one level in this thread
On January 14, 2004 at 16:49:29, Tord Romstad wrote: >Hi Ed, > >On January 14, 2004 at 16:26:42, Ed Trice wrote: > >>>Have you considered trying MTD(f) instead of PVS? I am not sure it is any >>>more efficient in practice, but it is easier to code, and has the additional >>>benefit of making you feel different, original, interesting, intelligent, >>>handsome and attractive. > >I forgot to include "brave" and "charming" in the list of adjectives. MTD(f) >is guaranteed to be at least as effective for attracting the opposite sex as >most of the products the spammers try to sell you. > >>Well Aske Plaat would love to hear that :) >> >>But doesn't MTD(f) trigger a great deal of researches? I remember trying that >>once and it bloated the tree. > >The whole idea of MTD(f) is that most of the re-searches will be extremely fast >because your hash table is packed with upper and lower bounds which give you >lots of instant cutoffs everywhere in the tree. > >But there are also ways to reduce the number of re-searches. Plain >MTD(f) as described in Plaat's paper never worked well for me, but >adding what is commonly known as a "convergence accelerator" improved >the situation a lot. When the search fails in the same direction more >than once, I increase the step size. If it still fails in the same >direction, I increase it even more. This continues until I finally manage >to make the search fail in the opposite direction. Doing like this also >gives you an additional advantage: You will often have an upper *and* >a lower bound for the root score. These bounds can be very useful for >pruning decisions. > >Another simple trick is to reduce the resolution of your evaluation >function. In my pre-MTD(f) days, I used pawn=128. I still use pawn=128 >as the internal unit in my evaluation function, but before returning >the final score I divide the score by 2. This simple change made my >search noticably more efficient. Did you try other divisors besides 2?
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