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Subject: alpha-beta is silly?

Author: Inmann Werner

Date: 02:03:32 06/02/98

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

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.

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


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