Author: Robert Hyatt
Date: 19:40:39 07/13/01
Go up one level in this thread
On July 13, 2001 at 16:50:26, Uri Blass wrote: >On July 13, 2001 at 14:25:23, Robert Hyatt wrote: > >>On July 13, 2001 at 12:28:01, Steve Maughan wrote: >> >>>I'm thinking of implementing double null move in my program. Now as far as I >>>know the most conventional way is to do the normal null move search and if there >>>is a cutoff follow it with a normal search at reduced depth to confirm no >>>zugwag. However I do remember that someone here (Vincent?) outlined a different >>>way of doing double null move. Is there another way? If there is, what are the >>>pros and cons of each? >>> >>>Thanks, >>> >>>Steve >> >> >>That's the gist of it. If the position is a zugzwang position, the second >>null-move search will fail high, which will cause the first to fail low and >>you don't run into the zug problem. >> >>The downside is the cost. The second null will fail low most of the time and >>just generate wasted nodes. >> >>The other downside is that not all null-positions are zugzwang problems. In >>fact, most null-move problems are caused by the R-value which bring the horizon >>too close to spot a tactical threat. Double null won't find any of those... >> >>So you expend quite a bit of effort, to eliminate one small part of the total >>problem... > >If you search to clearly reduced depth(for example before normal search with >null move pruning to depth d when d>=6 you search without null move to depth >d/2-2) then you may be less than 1% slower. > >I believe that it is a good deal to be 1% slower in order to avoid not seeing >simple zunzwangs. > >I guess that you may earn 3 elo from not falling in some zunzwangs and lose only >1 elo from being slightly slower. > >Uri It is far worse than 1%, as you try a null move after _every_ null move, except you never do 3 in a row. If you are searching to 14 plies, and you try a null move at ply=2, remaining depth would be 9 (12 - R=2 - 1). If you do a null-move search at ply=3, remaining depth would be 6 (9 - R=2 - 1). A 6 ply search is non-trivial. Do a bunch of them and it is _really_ non-trivial...
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.