Author: Jeremiah Penery
Date: 05:09:35 11/06/99
Go up one level in this thread
On November 06, 1999 at 07:19:19, Dan Homan wrote:
>Ok, your standard null-move code looks something like this....
>
> search(position current, int alpha, int beta, int depth) {
>
> .....
> position next;
> int score;
>
> /* null move */
> if( /* conditions to decide if null-move is appropriate */ ) {
> next = makeNull(current);
> if(depth >= R+1) {
> score = -search(next, -beta, -beta+1, depth-R-1);
> } else {
> score = -Qsearch(next, -beta, -beta+1);
> }
> if(score >= beta) return(beta);
> }
>
> .....
>
> }
>
>I simply modified the null move code to look like
>
> /* null move */
> if( /* conditions to decide if null-move is appropriate */ ) {
> next = makeNull(current);
> if(depth >= R+1) {
> score = -search(next, -beta, -beta+1, depth-R-1);
> } else {
> score = -Qsearch(next, -beta, -beta+1);
> }
> /* verification search */
> if(score >= beta && depth >= R+1) {
> next = current;
> set flag for no null move on next search;
> score = search(next, beta-1, beta, depth-R-1);
> }
> if(score >= beta) return(beta);
> }
>
>You can see that the verification search is just 3 or 4 lines of code.
>All it does is search the current position to a reduced depth with
>no null move.... this only happens when the null move is going to force
>a fail high, and it should confirm that we are not in zug. The time spent
>doing these verification searches is very small, so I think this might
>be a good addition. I still have to do tests on those positions you
>posted.
I have done something also quite simple to solve this problem (in Crafty). I
simply put "if (depth>6)" before the null-move section of the code, so that the
first 6 plies of depth will not use null-move. I may try to vary this a bit.
Your verification search probably is much better, though, so I will try to
implement it. My approach does allow Crafty to solve this position, however. :)
Jeremiah
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