Author: Robert Hyatt
Date: 08:13:05 09/03/04
Go up one level in this thread
On September 03, 2004 at 00:14:01, Stuart Cracraft wrote:
>On September 02, 2004 at 21:21:41, Robert Hyatt wrote:
>
>>On September 02, 2004 at 16:44:58, Stuart Cracraft wrote:
>>
>>>On September 02, 2004 at 15:31:31, martin fierz wrote:
>>>
>>>>On September 02, 2004 at 09:45:25, Michael Henderson wrote:
>>>>
>>>>>On September 02, 2004 at 02:39:28, martin fierz wrote:
>>>>>
>>>>>>On September 01, 2004 at 10:11:18, Uri Blass wrote:
>>>>>>
>>>>>>>On September 01, 2004 at 05:57:25, martin fierz wrote:
>>>>>>>
>>>>>>>>On September 01, 2004 at 00:51:47, Stuart Cracraft wrote:
>>>>>>>>
>>>>>>>>[snip]
>>>>>>>>
>>>>>>>>Muse on P4 2.4GHz finds the mate at ply 6, failing high on Qxf4 after 0.7
>>>>>>>>seconds (not shown in the logfile).
>>>>>>>>
>>>>>>>>the reason it can solve this at such a low search depth is probably twofold, the
>>>>>>>>first is that it generates checks in qsearch on the first ply of the qsearch (so
>>>>>>>>when you drop directly into qsearch with a nullmove, it will see Rh8# every
>>>>>>>>time), the second is probably that it is using mate-threat extensions.
>>>>>>>>
>>>>>>>>cheers
>>>>>>>> martin
>>>>>>>
>>>>>>>Do you get 2 plies only by mate extensions?
>>>>>>>In order to do it you need to extend 2/3 ply for mate threat.
>>>>>>>
>>>>>>>The line 1.Qxf4 Bxf4 2.Rxh5 gxh5 3.Rxh5 Bh6 4.Rxh6 is 7 plies and qsearch here
>>>>>>>does not see mate because it is black to move so I need 8 plies even if I
>>>>>>>disable pruning by evaluation.
>>>>>>
>>>>>>hi uri
>>>>>>
>>>>>>the reason must be that after 2.Rxh5 i get a mate threat extension and after
>>>>>>3.Rxh5 again, and since i do a full ply for that, my program sees it.
>>>>>>
>>>>>>cheers
>>>>>> martin
>>>>>>
>>>>>>>
>>>>>>>With pruning by evaluation latest movei get it only in 10 plies but I think to
>>>>>>>change my pruning to make it see it faster.
>>>>>>>
>>>>>>>Uri
>>>>>
>>>>>is recapture extension also playing a role here?...if that applies.
>>>>
>>>>it doesn't apply for me, but it probably depends on what an engine would
>>>>classify as a "recapture". some people might call any sequence of two captures
>>>>on the same square a recapture, for me a recapture is only if a piece of the
>>>>same value is recaptured. this isn't the case here.
>>>>
>>>>cheers
>>>> martin
>>>
>>>I consider a recapture to be a capture that restores the root material
>>>difference to what it was at ply = 0, before the search.
>>>
>>>Stuart
>>
>>
>>That is no good. The starting position comes right after I played BxN. It is
>>your move and you start the search. Material score is -3 for you. After you
>>make the re-capture at ply=1, I play RxR at ply=2. Score = -5. You play RxR to
>>make the score 0 again. 0 != -3 so you don't extend.
>
>Your example convinces. I discarded it and reclassify recapture extension
>as extend on 2nd capture on the same square.
>
>Didn't give a boost on the test suite though.
>
>Stuart
I am no longer sure that the recapture extension is even any good. It worked in
the days of 8 ply searches. But today I am not sure. Ken Thompson was the
first to use it that I know of, in 1983. He later decided it was bad. Here is
one position where it helps:
[D]2r2rk1/1bqnbpp1/1p1ppn1p/pP6/N1P1P3/P2B1N1P/1B2QPP1/R2R2K1 b - - 0 1
That is from the kopec-bratko test, position 22, correct move is Bxe4.
Crafty with recapture extension: (750mhz PIII laptop)
5 0.06 0.00 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4
5-> 0.15 0.00 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4
6 0.24 -0.02 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4 Rfe8
6 0.41 -1 1. ... Bxe4!!
6 0.48 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7
6-> 0.51 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7
7 0.65 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7
7-> 0.71 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7
8 1.00 -0.50 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Bxf6 Nxf6 5. Nxb6 Rxe4 6. Rac1
8-> 1.17 -0.50 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Bxf6 Nxf6 5. Nxb6 Rxe4 6. Rac1
9 1.99 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7 6. Bc3 a4
9-> 2.17 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7 6. Bc3 a4
time=2.18 cpu=87% mat=0 n=782537 fh=94% nps=358K
ext-> chk=3964 cap=3294 pp=27 1rep=90 mate=0
and crafty with recapture extension set to zero:
5 0.06 -0.04 1. ... Nh5 2. Qe3 Bf6 3. Bc3 Nc5
5-> 0.10 -0.04 1. ... Nh5 2. Qe3 Bf6 3. Bc3 Nc5
6 0.19 0.00 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4
6-> 0.29 0.00 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4
7 0.44 -0.02 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4 Rfd8
7-> 0.58 -0.02 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4 Rfd8
8 0.90 0.00 1. ... Nh5 2. Qe3 Bf6 3. Bxf6 Nhxf6
4. Qf4 Nh5 5. Qg4
8 1.80 -1 1. ... Bxe4!!
8 2.02 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7
8-> 2.07 -0.58 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Rxe4 5. Nxd7 Nxd7
9 2.79 -0.69 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Nxb6 5. Bd3 Rc5
9-> 2.98 -0.69 1. ... Bxe4 2. Bxe4 Qxc4 3. Qxc4 Rxc4
4. Nxb6 Nxb6 5. Bd3 Rc5
time=3.00 cpu=87% mat=0 n=1016538 fh=93% nps=338K
ext-> chk=4568 cap=4045 pp=33 1rep=125 mate=0
it finds Bxe4 about 4.5X faster with recapture than without...
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.