Author: Robert Hyatt
Date: 07:25:16 09/28/04
Go up one level in this thread
On September 28, 2004 at 00:01:15, Stuart Cracraft wrote: >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 There is the problem. If you can't return a score outside alpha/beta window, this threat detection will not work. 99.99999% of the time alpha is > MATE. You have to make your null-move search return a score < alpha in this case so that when it fails low, you notice that not only did not moving look bad, it got you mated instantly. If you can't return a score < alpha from the next ply, the mate threat won't work. >== -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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