Author: Andrew Williams
Date: 06:54:16 04/10/02
Go up one level in this thread
On April 10, 2002 at 09:14:48, Steve Maughan wrote:
>Andrew,
>
>>I don't understand what you mean by the "fail-soft move"?
>
>This is the move that gets the highest score when all moves fail low i.e it will
>have a score below alpha but may possibly be the best move. Ed Shroeder did
>store this move in the hash table but from Rebel 10? onward found it better to
>store 'nil'. I wonder if in this situation, the lack of moves stored in the
>hash for positions resulting from - say Qb8+, that freezes the search of many
>engines.
>
Aha! If I'd stopped to think, I'd have worked out what you meant. I don't store
a move in such situations.
>>It doesn't take PostModernist (on my Athlon 1200) very long at all to see the
>>problem with Qxh6:
>>
>>10> 198 0 14906 1.Qxh6 b4 2.Qh3 h5 3.Kg3 Nf5 4.Kf4 Kf7
>>10= 215 0 41916 1.Qxh6 Ne6 2.Kg3 b4 3.Kf2 f5 4.Ke2 a4 5.Qh2
>>11> 208 0 75603 1.Qxh6 Ne6 2.Kg3 b4 3.Kf2 a4 4.Qh2 f5 5.Qd6
>>11= 214 0 79964 1.Qxh6 Ne6 2.Kg3 b4 3.Kf2 a4 4.Qh2 f5 5.Qd6
>>12> 214 0 99721 1.Qxh6 Ne6 2.Kg3 b4 3.Kf2 a4 4.Qh2 f5 5.Qd6
>>12= 219 0 139014 1.Qxh6 Ne6 2.Kg3 b4 3.Kf2 a4 4.Qh2 f5 5.Qd6
>>13> -522 2 513766 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 f5 4.Kf4 Qd6
>> 5.Kg5 a4 6.Qxa4 Qg3 7.Kf6 Qxe3
>>13= -419 4 746241 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 h5 4.Kg3 Qd6
>> 5.Kh3 Qd8 6.Qb7 g5
>>14> -439 6 1198282 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 h5 4.Kg3 Qd8
>> 5.Qb7 f5 6.Kh3 g5 7.Kg3 h4 8.Kh3
>>14= -429 6 1264249 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 h5 4.Kg3 Qd8
>> 5.Qb7 f5 6.a3 g5 7.a4 h4 8.Kh3
>
>This is impressive!! I notice that the PV from ply 12 does not include Nh5,
>which is essential to meaningfully reject the position. Does PostModernist
>revert to another move (Qb8) instantly due to the heavy fail low? Does
>PostModernist recognise that the Queen is trapped after Nh5?
>
My program recreates its PV from the hash table, and it only extracts it at
certain points (first fail-high, new best move and completed iteration). I've
quickly changed my MT driver to show a bit more information about fail-lows:
11= 214 0 79964 1.Qxh6 Ne6 2.Kg3 b4 3.Kf2 a4 4.Qh2 f5 5.Qd6
12> 214 0 99721 1.Qxh6 Ne6 2.Kg3 b4 3.Kf2 a4 4.Qh2 f5 5.Qd6
12< 221 0 138235 1.Qxh6 Nh5
12< 220 0 139014 1.Qxh6 Nh5
12= 219 0 139014 1.Qxh6 Nh5
13< 45 1 177912 1.Qxh6 Nh5
13> -522 3 513766 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 f5 4.Kf4 Qd6
5.Kg5 a4 6.Qxa4 Qg3 7.Kf6 Qxe3
13< -417 4 730785 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 h5 4.Kg3 Qd6
5.Kh3 Qd8 6.Qb7 g5
13< -418 4 746241 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 h5 4.Kg3 Qd6
5.Kh3 Qd8 6.Qb7 g5
13= -419 4 746241 1.Qb8 Ne8 2.Qxe8 Qf8 3.Qxb5 h5 4.Kg3 Qd6
5.Kh3 Qd8 6.Qb7 g5
You can see that the last thing it sees about Qxh6 is Nh5. I have some queen
trapping code in PM, but it's been commented out for some time now. So I'm not
sure why PM is fast in this position. I guess the results of those other
programs beg the question, how long does it take to see Nh5 if you show them the
position after Qxh6? PM sees it in well under one second. Here's the position
after Qxh6:
[D] 6k1/6np/5ppQ/pp1p4/3Pp1K1/4P3/P7/8 b - - 0 1
Cheers
Andrew
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