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Subject: Re: How I Learned to Stop Hating 141

Author: Tord Romstad

Date: 07:47:38 09/03/04

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On September 03, 2004 at 10:14:53, Stuart Cracraft wrote:

>On September 03, 2004 at 09:47:26, Jan K. wrote:
>
>>You should look for bugs in your search....i find the move even with no
>>extensions but the threat extension set to 1/2 ply and no checks in qsearch.
>>Takes 60 seconds and almost the same number of nodes like your full search.
>
>Tord said something about having the null move search a window
>wider than -beta+1,beta and and then testing the return value
>against alpha-MARGIN. If less than that, a faillow and then
>extending.

This was in the context of BM extensions, not mate threat extensions.  For
mate threat extensions, there is no reason to use a wide window for the
null move search.  The only thing you need to remember is that if you
use a fail-hard search, you must remember to return exact scores instead
of bounds if the exact score is a mate.

>Has anyone else with PVS search implemented mate. Can you just
>include your code fragment in reply to this. I have programmer's
>block.

Sure.  Here is the null move part of the code in my new engine (which
uses PVS), with some irrelevant noise removed in order to make it easier
to read.  The BM extension is not yet implemented.

  if(nullmove && Ply>0 && !ss->check && !mate_threat && ss->eval >= beta &&
     ss->material[WHITE]>0 && ss->material[BLACK]>0) {

    make_nullmove();
    nullvalue = -search(-beta, -beta+1, depth-4*PLY, 0, 0);
    unmake_nullmove();

    if(nullvalue >= beta) return nullvalue;
    if(nullvalue <= -MATE_VALUE+Ply+2) mate_threat = 1;
  }

Tord



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