[Computer-go] Semeais

[Stefan Kaitschick]

I have also advocated this, comparing it to quiesence search in chess.
I still think this would be effective if done well.
Actually I think it is actually critical for high level play.
Because permutating between multiple semeais in all parts of the tree 
will always kill any amount of computing power available.
There are problems that go beyond spotting local semeais and playing the 
correct moves.
You artificially remove ko threats, and you also change ladders.
So in some situations the preliminary cleanup would need to be partially 
undone - very messy.
Perhaps these preliminary moves would need a different status, something 
like "as good as played"
That is what humans do, although I admit that that has been a poor 
indicator for mc programming.

Stefan

Am 13.01.2011 12:52, schrieb Kahn Jonas:
> By the way, has anybody tried the most basic way to settle semeais in
> playouts? I mean:
> * Spot semeais (not basic at all, but probably necessary for almost all
> approaches).
> * Play all the moves in the semeai before going to usual playouts.
>
> Of course this would primarily be for semeais with one-tempo difference.
>
> This gives a systematic advantage to the player who wins the
> semeai. But I don't know if it would have that much influence on the
> playouts. After all, they do not take ko threats into account.
>
> Jonas, for the barbaric why-don't-you-use-this-way that really does not
> work association.
>
>
>> Hi Petr and Jean-loup,
>>
>> I think Erica might drop to 2d if using the same time setting of Pachi2
>> (over 20mins SD).
>> The semeai in the bottom-left of this game is very interesting:
>> http://files.gokgs.com/games/2011/1/13/pachi2-BOThater36.sgf
>>
>> I believe, we must solve this kind of long-semeai to make our programs
>> reach high dan.
>>
>> Aja
>>       ----- Original Message -----
>> From: Jean-loup Gailly
>> To: computer-go at dvandva.org
>> Sent: Thursday, January 13, 2011 7:20 PM
>> Subject: Re: [Computer-go] pachi2
>>
>> Here is some preliminary information on the distributed version of
>> pachi.
>> Petr (pasky) and I will publish all the details later, this is just
>> to give
>> you an idea of what we are doing. Pasky is the main author of pachi
>> and
>> wrote most of the single machine code. I wrote the distributed code
>> and
>> some other improvements.
>>
>> All the code, including the distributed code, is GPL and available
>> at
>> http://repo.or.cz/w/pachi.git/
>>
>> The distributed pachi uses simple tcp/ip sockets, not MPI. This
>> makes it
>> portable to many environments. A master process receives stats
>> updates
>> regularly from all the slaves and distributes the aggregated
>> updates back
>> to all slaves. The master-slave protocol is specific to pachi but
>> it is
>> rather simple. It is fault tolerant: if a slave dies, the master
>> will send
>> again the whole game to the new slave that will replace it. If the
>> master
>> dies, I ignore the current game and restart a new one when doing
>> test
>> runs. If the master dies when running for KGS, I kill the kgsGtp
>> program
>> and start a new one; KGS then sends again the partial game and we
>> continue
>> from there.
>>
>> I measured scalability both on a single machine and in distributed
>> mode. All the details will be published, but here is a summary.  In
>> single
>> machine mode, doubling the number of cores gains roughly 100 elo or
>> one
>> stone. (I measured one stone to be approximately 100 elo).  This is
>> true up
>> to the number of cores I can test (20 per machine, other cores are
>> reserved
>> for the OS and other apps).
>>
>> In distributed mode doubling the number of machines initially gains
>> approximately 50 elo (half a stone) up to 8 machines.  Above this
>> we
>> quickly hit a scalability limit and the best result so far is with
>> 64
>> machines; this is the configuration used for the KGS tournament
>> (starting
>> at round 4) and on KGS right now. 128 machines are currently much
>> worse
>> than 64.
>>
>> Preliminary analysis of the lost games shows that the current code
>> has inherent scalability limits because the playouts are biased.
>> When the playouts incorrectly judge the life status of a group,
>> the results will be bad no matter how many cores and machines
>> work on it. We are of course working on this to eliminate these
>> scalability limits.
>>
>> Pachi has benefited enormously from ideas published on the
>> computer-go
>> mailing list and in many papers.  By making its source completely
>> open we
>> hope to encourage further progress in this area.
>>
>> Petr and Jean-loup
>>
>> ________________________________________________________________________________ 
>>
>>
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