Author: Stuart Cracraft
Date: 13:35:05 09/25/04
Go up one level in this thread
On September 25, 2004 at 16:02:08, Andrew Platt wrote: >On September 25, 2004 at 10:30:52, Rick Bischoff wrote: > >>Hi, >> >>I am confused about the mate threat extension. I have the following code: >> >>search ( depth, alpha, beta ) >> >>->check extension >>->else pawn extension >> >>->if depth <= 0 do the queiscent >> >>->if checkReps return draw >>->if insufficnetMaterial return draw >> >>->Probe the hash table and return if good >> >>->if not in check and depth>3 and last move was not null and material is ok: >>->-> do null move >>->-> x = -search(depth - 3, -beta, -beta +1 ) >>->-> undo null move >>->-> if ( x >= beta ) return beta >>->-> if ( x < (-MATE+MAXPLY) ) cout << "found mate" >> >>->normal alpha/beta stuff >> >>end search >> >>"found mate" never gets printed out in WAC141 unless I change the null move to a >>full width search... Why? Well, I shouldn't say never, but I let it run to ply >>9. > >if (x >= beta) return beta > >means that you don't return the actual scores, just the cutoff. This is fine >until you try to detect threats. Then you need to return the actual scores >because only those will have the mate in them. > >In WAC 141 you should hit a bunch of mate threat extensions on the way to the >lowest ply because each time your Rooks take a pawn, and then the bishop, you >should trigger one. In my search it still isn't enough to counteract the drop >into qsearch where I don't consider checks. I've given up on generating the mate >score in a short time right now (I have plenty of other problems!). It's enough >that the first few plies in the PV are correct so if it actually hit it, it >would find it. Of course that only works here because it turns out that the >Queen sacrifice is good more material as well as mate! > >Andy. So do you solve WAC 141 in a reasonable amount of time? I don't and my code returns all values, does a null move with -beta,-alpha, checks if the returning value is equal to -MATE+ply+2 to extend (but doesn't extend it if already in check), and I return -MATE+ply when in check in the main search. In quiescence, I pass back to the main search if in check, but I don't search checking moves unless they are captures. Anyway, with the above, WAC 141 is out of reach and no one has been able to help it!
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