Author: J. Wesley Cleveland
Date: 14:00:10 06/04/01
Go up one level in this thread
On June 01, 2001 at 13:59:11, J. Wesley Cleveland wrote:
I have been thinking about fail high's and fail low's. If you have a fail high,
and you have used a significant portion of the time available for this move (>
25% ?), you should just make the move without further searching, as you will not
have time to resolve the fail high and investigate other moves anyway.
Fail low's are a different problem. When you get a fail low, what you know is
that the current move has an upper bound at ply n of the ply n-1 value - window
while all other moves have an upper bound at ply n-1 of the ply n-1 value. It
seems it might be better to search some of the other moves before re-searching
this one.
This leads to a crafty question. In search.c, if all the values are < alpha (a
fail low), the value returned is alpha and not MAX(values). Why is this ?
>On May 31, 2001 at 10:44:18, Robert Hyatt wrote:
>
>>On May 31, 2001 at 08:56:33, Gian-Carlo Pascutto wrote:
>>
>>>On May 30, 2001 at 15:14:46, Robert Hyatt wrote:
>>>
>>>>3. When I fail high, I just relax
>>>>beta to +infinity, rather than the tiered approach I used in Cray Blitz. If
>>>>there are lots of mates here, that are not forced, the program still has to
>>>>search them all out as with +infinity, you get zero beta cutoffs at positions
>>>>where white is to move, until you establish a better beta value after a lot
>>>>of searching.
>>>
>>>Silly question...why don't you do it in Crafty? It's not like it's
>>>hard to code, and it gives real benefits.
>>>
>>>I use the CB approach after you once described it here or on rgcc and
>>>it's saved my ass a dozen times...
>>>
>>>--
>>>GCP
>>
>>
>>That is actually a good question. I guess I have simply not stopped to think
>>about it, but it was obviously a reasonable idea. Harry had this one ugly
>>position that at depth=12 would fail high, but we could not get a score back
>>from ever. We discovered that the problem was that if we relaxed beta to +inf,
>>about 90% of the positions were mates. Very deep mates. But not forced. When
>>we put in the tiered fail-high, the problem went away. It has been on my to-do
>>list for years, but I simply haven't gotten to it...
>
>It appears to be trivial to do. I put the following code in iterate.c
>
> int failinc[4] = {150, 350, 1000, MATE};
> int failhi = 0;
> root_beta += failinc[failhi++];
> if (root_beta> MATE+1)
> root_beta=MATE+1;
>
>and it speeded up the result on this problem about 100 fold. It certainly needs
>more testing and tweaking, but definitely seems worth looking at. Here are snips
>from the log files.
>
>before the change
>
> 13 31.70 3.39 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. Rh7 g5 7.
> f7 Qxh8 8. Rxh8+ Kxf7 9. Rxc8 g4 10.
> Kf2 Kf6
> 13-> 40.06 3.39 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. Rh7 g5 7.
> f7 Qxh8 8. Rxh8+ Kxf7 9. Rxc8 g4 10.
> Kf2 Kf6
> 14 48.98 ++ 1. Rxh7!!
> 14 121:42 4.01 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. f7 Qxh8
> 7. Rxh8+ Kxf7 8. Rxc8 Kg7 9. Kg2 g5
> 10. Bxg5 Rxb2+ 11. Kg3 e5
> 14-> 122:06 4.01 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. f7 Qxh8
> 7. Rxh8+ Kxf7 8. Rxc8 Kg7 9. Kg2 g5
> 10. Bxg5 Rxb2+ 11. Kg3 e5
>
>after
>
> 13 29.80 3.39 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. Rh7 g5 7.
> f7 Qxh8 8. Rxh8+ Kxf7 9. Rxc8 g4 10.
> Kf2 Kf6
> 13-> 37.29 3.39 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. Rh7 g5 7.
> f7 Qxh8 8. Rxh8+ Kxf7 9. Rxc8 g4 10.
> Kf2 Kf6
> 14 45.65 ++ 1. Rxh7!!
> 14 1:26 4.01 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. f7 Qxh8
> 7. Rxh8+ Kxf7 8. Rxc8 Kg7 9. Kh2 g5
> 10. Bxg5 Rxb2+ 11. Kg3 e5
> 14-> 1:54 4.01 1. Rxh7 Kxh7 2. Rh2+ Kg8 3. Qh4 Bxf6
> 4. exf6 Kf8 5. Qh8+ Qg8 6. f7 Qxh8
> 7. Rxh8+ Kxf7 8. Rxc8 Kg7 9. Kh2 g5
> 10. Bxg5 Rxb2+ 11. Kg3 e5
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