Computer Chess Club Archives




Subject: Re: Finding mate in the quiesce search

Author: Scott Gasch

Date: 12:43:00 08/24/04

Go up one level in this thread

On August 24, 2004 at 11:46:28, Robert Hyatt wrote:

>On August 24, 2004 at 11:34:31, Alessandro Scotti wrote:
>>On August 24, 2004 at 11:24:28, Anthony Cozzie wrote:
>>>On August 24, 2004 at 10:40:15, Alessandro Scotti wrote:
>>>>Ok but then you don't propagate the mate score out of the quiesce, right?
>>>And why not?
>>Well if I knew why I wouldn't be asking! (*) :-)
>>For now my reason is: there is no proof that a score is mate out of quiesce,
>>because quiesce doesn't examine all possible moves but only part of them. After
>>reading several replies this doesn't seem to be a popular opinion, though, but
>>that's how I see things at present...
>>(*) Hope English tenses are correct here!
>You miss the point.  I reach a node X, I can play a move which lets my opponent
>mate me, or I can stand pat.  The way around this is to notice that you are in
>check, and force the q-search to look at _all_ legal replies, and eliminate the
>"stand pat" option.
>Either way will produce a valid search result.  The latter will find forced
>mates more accurately of course...

To expand on what Bob said: also remember that if you have a position in the
qsearch where a side is in check BUT that side could have stood pat in the
previous qsearch positions then it does not really help to return a MATED score
now.  You know that because they chose not to stand pat before that they are
"down".  But because you have to assume that they had some other move option
than to continue trading / capturing when they chose not to stand pat, this
position is not forced and therefore not a true mate.

In my qsearch I do something like this:

    Are we in check AND has the side on move never had the chance to stand pat
    up to now?

    YES? Then do not allow a stand pat here and search all legal replies and
    possibly return a MATED-IN-N score here.  This position is forced.

    NO? Then allow a stand pat here and search a subset of the moves.  Do not
    return a MATED-IN-N score here even if you detect a mate because it is
    not forced.

This makes sense to me but I'd welcome any comments ;)


This page took 0.01 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.