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Subject: Re: alpha-beta is silly?

Author: Robert Hyatt

Date: 14:14:59 06/03/98

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On June 03, 1998 at 13:58:02, Thorsten Czub wrote:

>Sometimes - I guess - you have to make a weak move, that is NOT the best
>move in the position - to realize a plan of yours.
>Any grandmaster knows this. And of course any grandmaster understands
>the point that there are many similar moves within the draw-range.
>Chess-programmers often do not realize that you cannot really order the
>moves for BEST criteria. Since you will never find out accurate enough.
>
>So chess players know by experience that many moves are ok. Since they
>know this, they know that sometimes you can play a 2nd best or 3rd best
>move to
>realize a plan you need to win.
>I ask myself how alpha-beta can ever catch this behaviour !


It doesn't have to.  Alpha/beta doesn't catch "moves" it evaluates the
ultimate positions that *all* the moves lead to.  So it has no trouble
with a "weak move" that improves the position, because it is evaluating
the position at the end, not each individual move along the way.  If you
make moves that continually worsen your position, you lose.  If you make
moves that temporarily worsen your position, but eventually improve it,
you
may win.  Alpha/beta does this perfectly...

But no player I know would *ever* play the move he thinks is "second
best"
because he doesn't evaluate the move itself, he evaluates the resulting
position after that and several other moves are played.  And he *always*
makes the move that he believes leads to the best winning chances...
not
the move that looks best by itself...

and that's a perfect description of alpha/beta minimax search also...



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