Author: José Carlos
Date: 09:58:56 10/26/02
Go up one level in this thread
On October 26, 2002 at 12:43:02, Antonio Dieguez wrote:
>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".
>
>I don't quite follow you...
Ok, I'll try to make myself clear :)
We're at the root.
We search Nf3 (pv move) with alpha = 0, beta = 50
The search returns: score = 25
Now alpha = 25;
We try Nc3 with [alpha,alpha + 1] [25,26]
The search returns: score = 49
In the code you posted, as score (aux) is between alpha and beta, you now
research with a window [48,50] which most probably will fail high again, so you
waste time.
It's more logical to simple open the window with something like
[score,score+50] or [score,+INFINITY] without caring what beta is.
>I think that is what we call fail-hard or fail-soft
>alphabeta right? we can return a score greater than beta whenever the
>real score if at least this score, and something like that with alpha if
>we don't force the score to be at least alpha.
>
>so one could even write
>
>make
>aux = -alphabeta(board, -alpha-1, -alpha, depth-1);
>if(aux > alpha && aux < beta)
>{
> unmake & make(depends on the program)
> aux = -alphabeta(board, -beta, -aux+1, depth-1);
>}
>
>if (aux>alpha)
>{
> if (aux>=beta)
> {....return aux }
> alpha=aux
>...
>}
Ok, now I see the problem. You missed we're talking _at the root_.
José C.
>etc.
>
>antonio's usefull post.
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