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Subject: Re: alpha-beta is silly?

Author: Robert Hyatt

Date: 05:05:14 06/02/98

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On June 02, 1998 at 05:03:32, Inmann Werner wrote:

>Alpha - Beta is silly?
>
>Yesterday, I tried the LCTII Test Suite, position LCTFIN01. I was
>amazed, that INMICHESS (my program) needed  depth 9 to solve  the
>position. (running pawn)
>
>
>The position: Kc2/Pf2/kc4/Pg4/Pf5/Ph6/pb7/pf7/pg7/ph6
>Best Moves: 1.f6  2.gxf6 3.f4 4.b5 5.g5 6.fxg5 7.fxg5 8.hxg5 9.g6
>....->Queen
>
>I did not understand, why it did not recognize the running pawn in depth
>5. The 3 beating moves afterwards should be made in the quiet search,
>and then there is the running pawn!
>Nothing at all! I debugged the program.
>Very fast it was in depth 5 and then in the quiet search. There it made
>the 3 beating moves up to ply 8 and the calculatin function brought back
>-844. (more then 8 pawns)!! Super!
>But then alpha-beta threw the move away, because it was blacks move, and
>black did not want to get this bad rating. This continued until the
>normal search was in depth 9, although the black moves are forced.
>But think! This all is normal alpha-beta with no programming failure!
>
>Conclusion: alpha-beta does no moves, where the player who moves get a
>bad rating, especially in qiet search, although if the moves are forced.
>It thinks, if ist my move, it only can get better. (Something like a
>Null-Move thinking). On one side, this makes alpha-beta fast. On the
>other side, trivial things get moved behind horizon.
>If you try to change this, the program gets worse, because in most
>positions, above is right.
>

your analysis is wrong.  In the quiescence search, captures are *not*
forced, they are *optional*.  And one side *must* be able to stand pat
and not make a capture, else the score will be horrendously wrong...

So this is *not* an alpha/beta issue at all, it is a quiescence-search
paradigm that is completely unrelated to alpha/beta


>Is above conclusion correct?
>Has anybody thought deeper about this?
>
>Maybe, yesterday the first time, I understood alpha-beta.
>
>Besides: Fritz 4 also recognized the running Pawn in depth 9!
>
>Best Greetings
>
>Werner



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