Author: Robert Hyatt
Date: 07:10:27 08/31/01
Go up one level in this thread
On August 31, 2001 at 00:16:09, Robert Hyatt wrote:
>On August 30, 2001 at 21:58:04, Pham Minh Tri wrote:
>
>>Hi Bob,
>>
>>I am studying how Crafty closes the search window in the root search (file
>>searchr.c). I have learned much from your code. Thanks.
>>
>>There is a point I am unclear: updating beta. I am afraid that the search of
>>next moves may be faulty after updating it.
>>
>>Suppose a situation: original value of beta = 1000, a good move brings a value
>>of 200, so Crafty changes beta to value+40 = 240. The next move gives a better
>>value of 300. Crafty says the search is good and need not re-search with wider
>>window and then stop searching because of value>beta. It turns out there is no
>>bestmove. However, if program does not update beta (beta==1000), the search has
>>to redo and may find a bestmove (say, a move gives exactly 400).
>>
>>What do I miss here?
>>Many thanks,
>>Pham
>>
>>PS: Here is pseudo code after searching with window [-alpha-1, -alpha]. I marked
>>the unclear points by arrows.
>>
>> Search with window [-alpha-1, -alpha]
>>
>>==> if ((value > alpha) && (value < beta)) {
>> Re-search with window [-beta, -alpha]
>> }
>> if (value > alpha) {
>> root_value=alpha;
>> if(value >= beta) {
>> Update some thing
>> return value;
>> }
>> alpha=value;
>>==> beta=value+40;
>> root_beta=beta;
>> }
>
>
>It is too late to look at that tonight with any reasonable level of
>concentration. It looks wrong at first, and might well be something left
>lying around from testing something else somewhere in the past. I see no
>reason to tickle around with beta there. I will try to study it tomorrow
>to see if I can remember what was going on here...
The lines don't belong. I tried several positions and could not find one
where removing them changed anything, but they are definitely something left
over from old testing somewhere. They will not be in 18.11 when it is released.
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