Author: Tony Werten
Date: 23:08:40 04/28/04
Go up one level in this thread
On April 28, 2004 at 16:14:39, Gerd Isenberg wrote:
>On April 28, 2004 at 13:45:05, Ed Schröder wrote:
>
><snip>
>
>>What is double nullmove? I only know recursive nullmove allowing multiple
>>nullmoves. I also read about "allowing 2 nullmoves in a row". What are the
>>differences?
>>
>>I use recursive nullmove, not allowing the next ply after the nullmove to
>>nullmove. So:
>>
>> e2-e4
>> e7-e5
>> **-** // nullmove
>> d7-d5 // do no allow nullmove
>>
>>When I remove that check I get a few percent speedup, results look okay.
>>
>>Ed
>
>
>Hi Ed,
>
>yes Double Nullmove, suggested and invented by Vincent, allows to play two
>nullmoves in a row, to efficiently get rid of zugzwang problems. It is recursive
>too, and if i understand correctly, it works fine without any nullmove
>precondition:
>
> if (!inCheck)
> {
> if ( move2thisNode != null || move2ParentNode != null ) (
> val = -doNullMoveSearch(depth-1-R,...);
> if ( val >= beta ) return val; // return beta;
> }
> }
>
>May be Vincent may correct me.
>It seems that there is an implicit kind of IID with 2R-2 too.
Correct. Chech your hashtable again after the nullmove, if you didn't have a
best move before.
Then throw out IID.
Tony
>
>What i do (did?), is a conditional confirmation search with same depth reduction
>if a single nullmove fails high. To look whether there is at least one move
>equal or better than doing nothing. Pseudo code like this:
>
> if (!inCheck)
> {
> eva = evaluate(&thread,..); // thead is negative if eg. own pieces hang
> if ( move2thisNode != null && eva + thread - margin >= beta )
> (
> val = -doNullMoveSearch(depth-1-R,...);
> if ( val >= beta )
> { // nullmove cutoff?
> if ( !likely2haveZugzwang() )
> return val;
> if ( search(depth-1-R,...) >= beta ) // one may even try depth-2-R
> return val;
> // else zugzwang detected
> }
> }
> }
>
>Cheers,
>Gerd
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