Author: James Robertson
Date: 21:37:16 02/03/99
Go up one level in this thread
On February 04, 1999 at 00:15:59, Robert Hyatt wrote:
>On February 03, 1999 at 22:54:36, James Robertson wrote:
>
>>Help!!
>>I am trying to implement null move into my program. Unfortunately, I have spent
>>a ton of time and gotton nowhere. I thought I had it when my program won it's
>>first ever game against EXchess, but realized it was a fluke when it hung first
>>a bishop and then a queen against Faile. Then I found a huge bug, and after
>>fixing, the null move doesn't seem to be speeding up the search at all. Anyway,
>>here is my AB code: what am I doing wrong?
>>
>>int AB (int wtm, int alpha, int beta, int depth, int ply, int do_null) {
>>
>> if (do_null && NotInCheck()) {
>> if (depth > 3) score = -AB(wtm^1, -beta, -beta+1, depth-3, ply+1, false);
>> else score = -Quiesce(wtm^1, -beta, -alpha, ply+1);
>> if (score >= beta) return beta;
>> }
>>
>> GenMoves();
>> while (moves){
>> MakeMove();
>> score = -AB(wtm^1, -beta,-alpha,depth-1,ply+1,true);
>> UnMakeMove();
>> if (score > alpha) SavePV();
>> if (score >= beta) return beta;
>> }
>>}
>>
>>Thanks for any help!
>>
>>James
>
>
>I'd suggest looking at crafty source, module=search.c, near the top. Which
>shows this...
>
>A couple of things I see however...
>
>1. you have to be very careful with things like en passant status. Since
>a null-move _must_ clear this before going to the next ply...
Ok.
>
>2. don't do this if there are no pieces (only pawns) left for the side on
>move, otherwise zugzwang will cause problems. Do it _carefully_ if there is
>only one piece for the side on move.
Ok, sounds cool.
>
>3. don't forget to handle the EP status in your hash key if you keep it there
>(as I do).
I don't have hash tables yet, but when I get them I'll watch out for this. I
tried out Mr. Moreland's suggestions, and things look better. Thanks for your
help too!!
James
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