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Subject: Re: mate threat extension/null move

Author: Uri Blass

Date: 10:17:27 10/01/04

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On October 01, 2004 at 12:43:48, Stuart Cracraft wrote:

>On September 29, 2004 at 22:04:41, Don Beal wrote:
>
>>On September 29, 2004 at 10:23:20, Stuart Cracraft wrote:
>>
>>>For this one, I am *paying* $50 to the first person who can point out
>>>the solution to make my mate threat work and make the Win at Chess #141
>>>problem time drop from 95 seconds on a 1ghz p3 to ~30 seconds or less
>>>on the same box.
>>
>>$50!  :-)  I'll have a go.
>>
>>In the code you posted,
>>instead of:
>>  if (!threat && donull && (material[stm^1]>weights[0][stm^1][rook])
>>      && !checked && !inpv) {
>>use:
>>  if(!threat && donull && !checked) {
>>and instead of:
>>  if (value >= beta) {
>>use:
>>  if (value >= beta
>>  && !inpv && (material[stm^1]>weights[0][stm^1][rook]) ) {
>>
>>
>>The idea of these changes is to apply the null move search
>>(and hence get the mate threat extension working) in the
>>pv as well as other variations, while still preventing
>>you pruning in the pv or believing in null move betas
>>when material is too low.
>>
>>
>>In the unlikely event that:
>>(a) I have understood your code
>>(b) I have correctly diagnosed a problem
>>(c) my fix does not conflict with other things you do
>>(d) it achieves your desired 3-fold speedup on 141
>>then the $50 will be gratefully received, but don't
>>send it to me - send it to the Steve Schwarz CCC
>>donation fund!
>
>Hi Don -- I remember reading your articles through the years
>especially that one on null move. Thanks for your interest.
>
>I did take your code and put it into my program and removed
>both Ross Boyd's and Uri Blass's ideas to test. Since they had
>already solved the problem of my slow WAC 141 from 95 down to
>5 seconds but Bob now tells me it's no good since it throws
>out the null move by disabling it for depth > 1 which is a
>very bad idea. So I can't name Ross nor Uri as receivers of
>the bet after all.

I only suggested to limit the recapture extension because the way that you use
it is clearly wrong.

correct recapture extension should not change much in 141.
Of course if you limit it to have recapture extension only in the first 5 plies
then it can help much and it is still better than do it everywhere but generally
it is not a good idea.

If the target is solving 141 and not productive recapture extension then you
have 2 ways:

1)having counter productive recapture extension.
2)having mate threats extensions and checks in the qsearch

Uri



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