Author: Tony Werten
Date: 03:36:35 04/20/04
Go up one level in this thread
On April 20, 2004 at 04:50:19, Tord Romstad wrote: >On April 19, 2004 at 20:38:47, Mike Siler wrote: > >>My program tries a null move search if >> >>1. it's not the endgame > >This is far too restrictive. Be careful about allowing null move pruning in >pawn endgames and endgames where one side has only the king left, but in more >complicated endgames the speed gain more than outweighs the risk of >occasionally overlooking a zugzwang. > >>2. it's not a PV node > >Have you tried removing this condition? > >>3. it didn't just make a null move > >This just complicates the search for no good reason, I think. Many people >avoid more than one null move in a row, but I don't unerstand why. I've >never seen any bad effect of allowing successive null moves. > >>4. it's not in check and wasn't in check on the previous ply > >The "check on the previous ply" condition should almost certainly be >dropped. > >>5. the remaining depth isn't so small that the reduced depth would take it into >>the qsearch > >This is also a bad idea, I'm afraid. It would render you null move search >much less effective. I know that some people (Bob, for instance) uses a >lower null move reduction factor when the remaining depth is small, but >I don't know any nullmovers who disable null moves entirely in this case. > >But you do not mention the most important condition of all: Only do null >move in nodes where you have a good reason to believe that you will fail >high! If the static eval is far below beta, doing a null move search is >almost certainly a waste of time. > >As a start, I think the following two conditions should be sufficient: > >1. Don't make a null move if the side to move is in check (or is threatened > by a mate in 1, if you have an easy way to detect this). > >2. Don't make a null move if the static eval is far below beta. Actually, you can drop 2 as well :) Move ordering is much better if you just nullmove everywhere. That way, you can also throw out IID. Tony > >Tord
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