Author: JW de Kort
Date: 23:16:49 03/24/99
Go up one level in this thread
On March 24, 1999 at 08:45:23, Robert Hyatt wrote:
>On March 24, 1999 at 06:03:26, JW de Kort wrote:
>
>>Hi Chess friends,
>>
>>I have a simple question concerning the quiescence search. Standar alpha-beta
>>usualy starts with something like
>>
>> if (depthh == 0)
>> return evaluate (position)
>>
>>most qsearches i have seen do not have thsi kind of ply depth termination. Now
>> i wonder how can a q search ever terminate? I have seen a question like this
>>before, but could some one please explain? What i'am afraid off is that my
>>qsearch will go on and on evaluating a line of play in wich white takes all the
>>pieces at the kingside, while black does the same on the queen side.
>>
>>Thanks in advance.
>>
>>Jan Willem
>
>
>Most of us replace the above with this:
>
> if (depth == 0)
> value=-Quiesce(-beta,-alpha,wtm^1, etc);
> else
> value=-Search(-beta,-alpha,wtm^1,depth-1,etc);
>
>Quiesce is a simple search that looks like this (details omitted but basic
>idea is present):
>
> int Quiesce(alpha,beta,wtm) {
> alpha=Evaluate(etc);
> if (alpha > beta) return(beta);
> while(more_captures) {
> MakeNextCapture();
> value=-Quiesce(-beta,-alpha,wtm^1);
> if (value > alpha) {
> if (value >= beta) return(beta);
> alpha=value;
> }
> }
> return(alpha);
> }
>
>
>the difference between Quiesce and Search is that Quiesce sets the lower bound
>to the current positional evaluation + material. Because we allow the current
>side to 'stand pat' and not play any move (capture only) if he doesn't want to.
>
>Search() doesn't allow one side to 'not move' as that is illegal. But here we
>use it to 'stop' the sequence of captures and exit, or else we can make a
>capture that helps our score, but then the opponent gets to decide whether he
>wants to 'stand pat' or make a capture in response.
>
>Hope that helps..
>
>If something isn't clear, feel free to ask, as there could easily be a typo in
>the above...
Thank you very much Mr. Hyatt for ypur reply. I think it is quite an achievement
of you to answer all these basic questions so promptly! I always learn a great
deal from them.
But i still have a question. How does this search terminate in a case were
both players can make equal captures in reply to the move of the other player?
Thanks again
Jan Willem!
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