Author: José Carlos
Date: 04:50:54 10/26/02
Go up one level in this thread
On October 25, 2002 at 21:27:18, Nagendra Singh Tomar wrote:
>On October 25, 2002 at 20:10:17, Nagendra Singh Tomar wrote:
>
>>Hello all,
>>
>>If we are using PVS search and assume that at the root, the 2nd move (searched
>>with a zero window) turns out to be the best move. Since we are passing a zero
>>window down to that subtree, at all the plys below, it will either fail-low or
>>fail-high, so none of the plies will update the PV. In this case we will get a
>>pv length of 1 (with only the root move in the PV).
>>Is this true whenever any move other than the first move tried at the root lies
>>on the PV.
>>How do we fill the PV in such cases ? using trans table ?
>>
>>regds
>>tomar
>
>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).
How you do the researches is up to you. I guess we all use some personal ideas
there.
Make sure the fail high is correct, rearching with [score,score+30] for
example. If that research fails low, forget tha move; if it's within score and
score+30, you have a new pv; if it fails high again, open the window to
+INFINITY or try small windows like [score,score+150] and then
[newscore,newscore+300]... Try your own ideas there, it's funny.
Dont forget that you can fail high with a,a+30 -> a+45 and then try a+45,a+100
and fail low... You muse be very careful about those cases. If you get sick of
that, try [-INFINITY,+INFINITY] ;)
José C.
>{
> score = -alphabeta(board, -beta, -score, depth-1);
> OR
> score = -alphabeta(board, -beta, -score+1, depth-1);
>}
>
>since the zero window search failed high and it returns
> score, this means that the true score is >= score.
> Now when we do a wide window search, if we want to store the PV
>properly we have to pass alpha value less than the possible
> score, else PV will not get updated (Note: PV gets updated only
> for nodes where score > alpha.). So we pass -score+1
>
>Am I right ?
>
>regds
>tomar
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