Author: JW de Kort
Date: 23:16:49 03/24/99
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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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