Author: Dan Newman
Date: 02:20:36 04/04/00
Go up one level in this thread
On April 03, 2000 at 19:53:41, KarinsDad wrote:
>On April 03, 2000 at 16:49:22, Dan Newman wrote:
>
>>On April 03, 2000 at 10:56:08, KarinsDad wrote:
>>
>>>On April 03, 2000 at 05:00:20, Jan Pernicka wrote:
>>>
>>>>On March 31, 2000 at 14:17:12, KarinsDad wrote:
>>>>
>>>>>
>>>>>Could someone please explain how they implement their SEE function, when they
>>>>>use it, and what they use it for?
>>>>>
>>>>>Or possibly a good web site that explains it.
>>>>>
>>>>>Any help is appreciated.
>>>>
>>>> Excuse me, could someone explain to me in several sentences what is
>>>> SEE function good for? Thanks
>>>> Jan
>>>
>>>
>>>Good luck.
>>>
>>>That is what my original post asks for and I did not receive any good answers.
>>>
>>>KarinsDad :)
>>
>>In Shrike I use the SEE everywhere to order the captures before I try them.
>>I don't use the SEE to do actual evaluation but do use it to prune losing
>>captures in the quiescence search and to delay trying losing captures in
>>the full width search. Currently I put losing captures at the tail end.
>>
>>Implemention. In my SEE I do some initial stuff to record the results of
>>the first capture which is fixed by the move in question. Then I create
>>a bunch of bitboards containing the remaining pieces that bear on the square
>>in question. Then I cycle through them "capturing" with less valuable pieces
>>first, more valuable later, alternating between sides. As I'm doing this I
>>knock out pieces that bear on the square but are blocked. I also determine
>>if pieces bearing on the square become unblocked and put them back in their
>>respective bitboards so that they will be found on a later pass. (The
>>machinery is fairly complicated and does a bit more than described above.)
>>All the while an array is being filled out with the current balance. After
>>all the attacking pieces of one side or the other are exhuasted and captured,
>>I quit making passes. At that point I "mini-max" the values in that array
>>to determine where one side or the other can simply stop and retain the best
>>advantage. The score at this point is the score returned by the SEE.
>>
>>-Dan.
>
>Thanks Dan. How do you min-max?
>
>For example, a knight is on the square and protected by a rook. Two rooks in a
>battery attack it. Rxn rxR Rxr wins a knight. However, after Rxn, the attacking
>side is winning a knight. After rxR, the defending side is winning a rook for a
>knight. After Rxr, the attacking side again is winning a knight.
>
>Since it flip flops, how do you know when to stop? Is it when your capture no
>longer wins for you (regardless of what your opponent's capture just won for
>him)?
>
>KarinsDad :)
First, I run out all the captures w/o stopping to create an array with running
totals (what I called current balance, above)--with the total from the view
point of the side that makes the capture:
Rxn 300 white is up 300
rxR 200 black is up 200
Rxr 300 white is up 300 again
where N=300, R=500. Then, starting at the tail end, I "minimax" up through
that array using the following bit of code:
while( ns ) {
if( seelist[ns] > -seelist[ns-1] ) seelist[ns-1] = -seelist[ns];
ns--;
}
(The running totals were maintained in seelist[]; ns starts out set to the
number of entries-1)
Then I return seelist[0].
I find that I don't really understand that bit of code above and have to
work it out with pen and paper (on several examples) to see what it does...
-Dan.
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