Author: Nagendra Singh Tomar
Date: 16:04:33 10/26/02
Go up one level in this thread
On October 26, 2002 at 12:27:46, José Carlos wrote:
>On October 26, 2002 at 12:07:16, Antonio Dieguez wrote:
>
>>>>score = -alphabeta(board, -alpha-1, -alpha, depth-1);
>>>>
>>>>if(score > alpha && score < beta)
>>> ^^^^^^^^^^^^^^^
>>>
>>> Don't use beta there. You just want to know you're above the pv score (which
>>>is alpha now).
>>
>>if I am not mistaken it depends on the exact writing.
>>
>>he can write
>>
>>make...
>>score = -alphabeta(board, -alpha-1, -alpha, depth-1);
>>if(score > alpha && score < beta)
>>{
>> unmake & make(depends on the program)
>> score = -alphabeta(board, -beta, -alpha+1, depth-1);
>>}
>>
>>unmake
>>
>>if (score>alpha)
>>{
>> blabla
>> if (score>=beta)
>> { update killer; update hash; etc. }
>>}
>>
>>-------------------
>>or he can write something like this?
>>
>>make
>>score = -alphabeta(board, -alpha-1, -alpha, depth-1);
>>if(score > alpha)
>>{
>> if (score>=beta)
>> { unmake; update killer; update hash; return beta; }
>> unmake & make(depends on the program)
>> score = -alphabeta(board, -beta, -alpha+1, depth-1);
>> unmake
>> if (score>alpha) // 'cause it could fail low right?
>> {
>> if (score>=beta)
>> { update killer; update hash; return beta; }
>> etc.
>> }
>>}
>>
>>I have written the first option, I think I can't make it prettier with the
>>second option or something else but may be you can write it better off corse.
>>
>>Ah if the search always return alpha or beta then that can change things.
>>
>>
>>antonio's usefull post.
>
> I don't quite follow. He's talking about the null window searches after the
>pv. He's searching [alpha,alpha+1] so he might fail high with alpha+1 or
>alpha+500, and beta isn't useful here at all. All you know if you fail high is
>"I've found a move that seems to be better than my current pv".
That <beta check is needed because if the score is >beta, then also we are not
interested in the score because we know that this is too good a score for us for
the opponent to allow .. so the opponent will not let us lead to the board where
we can play this move.. thats why we ignore for >alpha and >beta cases.
So you open the
>window and research to get a true score (note that you can also forget about the
>true score and keep searching the other moves with [alpha,alpha+1] hoping no
>other move fails high and trust your fh and go to the next ply).
> Beta only matters if you search [alpha,beta], this is, if it is one of the
>bounds.
>
> José C.
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