Author: Dann Corbit
Date: 12:42:27 01/27/04
Go up one level in this thread
On January 27, 2004 at 14:40:37, Tord Romstad wrote:
>On January 26, 2004 at 17:14:34, Dann Corbit wrote:
>
>> /* ----------==== INTERNAL ITERATIVE DEEPENING ====----------- */
>>
>> /* If we're not doing a NULL move and we don't have a hash move and we're
>> * at least 3 ply away from the quiescence search, then try to get a good
>> * guess for the best move by doing a shallower search from here. */
>> if (depth >= 3 && !do_null) {
>> w = search(on_move, ply, depth-2, alpha, beta, do_null, 1);
>> /* Re-search properly if the previous search failed low, so that we
>> * know we're getting a good move, not just the move with the highest
>> * upper bound (which is essentially random and depends on the search
>> * order.) */
>> if (w <= alpha)
>> w = search(on_move, ply, depth-2, -32500, alpha+1, do_null, 1);
>> }
>
>Hi Dann,
>
>Are you sure it is a good idea to re-search if the first IID search
>fails low? I have never tried this myself, but at first sight it
>doesn't look like a good idea to me. When the reduced-depth search
>fails low, it is likely that the full-depth search will also fail low.
>At fail low nodes, move ordering doesn't matter much, because you have
>to search all moves anyway.
Because it is used for move ordering, and because the depth is 2 plies below the
current search depth, it is a sure win. The cost is 1/400th of a full search,
and the win is a good guess for the pv node.
At least when I tested it in Beowulf it worked well. But I did not try it both
ways in Olithink.
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