Author: José Carlos
Date: 09:55:38 12/30/00
Go up one level in this thread
On December 30, 2000 at 12:37:07, Steve Maughan wrote: >In my program I have the following lines of code after the hash probe: > > if (CurrentHash.Bound = HASH_LOWERBOUND) then > begin > if (CurrentHash.Value >= Beta) then > begin > result := CurrentHash.Value; > exit; > end > //increase the value of alpha if lower bound is greater > else if CurrentHash.Value > Alpha then > begin > alpha := CurrentHash.Value; > PVLength := Ply; > end; Mmmm, wouldn't this node be _at least_ a PV node if a lower bound to its value is >alpha? So, if I'm wright, in this point you should research to see if the _real_ value is above beta, or eigther this is a PV node. > end; > if (CurrentHash.Bound = HASH_UPPERBOUND) then > begin > if (CurrentHash.Value <= Alpha) then > begin > result := CurrentHash.Value; > exit; Now, here, the search must stop and go to the next move, 'cause this is sure <alpha. > end > //see if beta can be lowered > else if CurrentHash.Value < Beta then > begin > Beta := CurrentHash.Value; And this is wrong. You can't modify beta here, cause you inherit beta from down level alpha, and it means a value high enough that the opponent wouldn't chose this branch. You're not allowed to modify beta inside the tree. Only alpha. José C. > end; > end; > >The bit that I'm not sure about and having problems with is the section that >adjusts the value of alpha and beta based upon the hash results. I'm getting >odd PVs and different values returned when I activate this section. > >Is it valid to raise the value of Alpha when the depth is sufficient and the >lowerbound is greater than Alpha? What happens to the PV? I'm just cutting it >off at the moment (i.e. PVLength := Ply). > >Likewise, is it valid to lower beta based on an upperbound? Again what happens >to the PV? At the moment I'm doing nothing as I cannot see that it's logical to >cut it off. > >All help and suggestions appreciated! > >Regards, > >Steve > >BTW the code is written in Object Pascal / Delphi!
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