Author: Stuart Cracraft
Date: 21:01:15 09/27/04
Go up one level in this thread
On September 27, 2004 at 18:17:19, Robert Hyatt wrote: >On September 25, 2004 at 16:35:05, Stuart Cracraft wrote: > >>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! > > >If you do mate threat right, you should find this quickly. Here is Crafty on a >single-CPU 2.8ghz PIV: > > 8-> 1.58 -1.20 1. Kf1 a5 2. Rxh5 gxh5 3. Rxh5 Re1+ > 4. Kxe1 Nxh5 5. Qg5+ Kf8 6. Qh6+ Kg8 > 7. Qxh5 > 9 3.91 -1.20 1. Kf1 a5 2. Rxh5 gxh5 3. Rxh5 Re1+ > 4. Kxe1 Nxh5 5. Qg5+ Kf8 6. Qh6+ Kg8 > 7. Qxh5 > 9 4.38 +1 1. Qxf4!! > 9 4.63 +3 1. Qxf4!! > 9 5.11 +M 1. Qxf4!! > 9 49.31 Mat06 1. Qxf4 Bxf4 2. Rxh5 gxh5 3. Rxh5 Bh6 > 4. Rxh6 Qh2+ 5. Kxh2 Kf8 6. Rh8# > 9-> 49.31 Mat06 1. Qxf4 Bxf4 2. Rxh5 gxh5 3. Rxh5 Bh6 > 4. Rxh6 Qh2+ 5. Kxh2 Kf8 6. Rh8# > >4 secs to find it. 49 secs to produce the mate score. > >With mate threat extension disabled (ext/mate=0 command) I see this: > > 10-> 20.95 -1.31 1. Kf1 Kf8 2. Rxh5 gxh5 3. Rxh5 Re1+ > 4. Kxe1 Nxh5 5. Qh6+ Ke8 6. Qxh5 Bf4 > 11 40.48 -1.08 1. Kf1 a5 2. Rxh5 gxh5 3. Rxh5 Re1+ > 4. Kxe1 Nxh5 5. Qg5+ Kf8 6. Qxh5 Bb4+ > 7. Kd1 Qd6 > 11 43.03 +1 1. Qxf4!! > 11 43.94 +3 1. Qxf4!! > 11 52.35 +M 1. Qxf4!! > 11 5:12 Mat06 1. Qxf4 Bxf4 2. Rxh5 gxh5 3. Rxh5 Bh6 > 4. Rxh6 Qh2+ 5. Kxh2 Kf8 6. Rh8# > 11-> 5:12 Mat06 1. Qxf4 Bxf4 2. Rxh5 gxh5 3. Rxh5 Bh6 > 4. Rxh6 Qh2+ 5. Kxh2 Kf8 6. Rh8# > > >SO it finds the right move 2 plies quicker, 10X faster, with than without the >mate threat extension... > >This with a simple q-search with no checks, no check evasion or anything else.. I obviously don't do mate threat right. Taking the result of the null move with -beta,-beta+1 or -beta,-alpha, or MINIMUM_INT,MAXIMUM_INT, and checking that result if < beta for == -MATE+ply+2 and extending by 1 obviously is not the right way to do mate threat. I tried endless variations of the above and nothing speeds up WAC 141 over my 95 second solution on a 1ghz P3 so I'll let it sit at this unless anyone can see through all that. I think I've been fairly straightforward about not having been able to get this mate threat working right. I know it is in various people's code but I find deciphering another chess program often doesn't give the insight I had thought and that silent suffering with my own code is "where it's at". Stuart
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