Author: Don Dailey
Date: 02:37:40 06/02/98
Go up one level in this thread
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. > >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 Hi Innman, I did not look at the position yet, but I know that Alpha/beta will not throw out a good move. One well known characteristic of alpha/beta is the fact that it will ALWAYS give you the same result as a full width search with no alpha beta. This is fact, so perhaps there is simply a bug. If the queening move occurs in the quies search, and you have a typical quies search where each side has the option to play a null move and stop, then the opponent will take this option rather than allow the program to queen. Look for these things. Another thing to try is a simple technique of moving forward. Play the correct first move and see how many it takes. Keep walking forward until it should see it with a 1 ply search and note its behavior. This might give you clues to find the bug, or understand what is going on. - Don
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.