[Computer-go] 9x9 is last frontier?

Álvaro Begué alvaro.begue at gmail.com
Tue Mar 6 12:23:06 PST 2018


Sorry, I haven't been paying enough attention lately to know what
"alpha-beta rollouts" means precisely. Can you either describe them or give
me a reference?

Thanks,
Álvaro.



On Tue, Mar 6, 2018 at 1:49 PM, Dan <dshawul at gmail.com> wrote:

> I did a quick test with my MCTS chess engine wth two different
> implementations.
> A standard MCTS with averaging, and MCTS with alpha-beta rollouts. The
> result is like a 600 elo difference
>
> Finished game 44 (scorpio-pmcts vs scorpio-mcts): 1/2-1/2 {Draw by 3-fold
> repetition}
> Score of scorpio-mcts vs scorpio-pmcts: 41 - 1 - 2  [0.955] 44
> Elo difference: 528.89 +/- nan
>
> scorpio-mcts uses alpha-beta rollouts
> scorpio-pmcts is "pure" mcts with averaging and UCB formula.
>
> Daniel
>
> On Tue, Mar 6, 2018 at 11:46 AM, Dan <dshawul at gmail.com> wrote:
>
>> I am pretty sure it is an MCTS problem and I suspect not something that
>> could be easily solved with a policy network (could be wrong hree). My
>> opinon is that DCNN is not
>> a miracle worker (as somebody already mentioned here) and it is going to
>> fail  resolving tactics.  I would be more than happy with it if it has same
>> power as a qsearch to be honest.
>>
>> Search traps are the major problem with games like Chess, and what makes
>> transitioning the success of DCNN from Go to Chess non trivial.
>> The following paper discusses shallow traps that are prevalent in chess.
>> ( https://www.aaai.org/ocs/index.php/ICAPS/ICAPS10/paper/downl
>> oad/1458/1571 )
>> They mention traps make MCTS very inefficient.  Even if the MCTS is given
>> 50x more time is needed by an exhaustive minimax tree, it could fail to
>> find a level-5 or level-7 trap.
>> It will spend, f.i, 95% of its time searching an asymetric tree of depth
>> > 7 when a shallow trap of depth-7 exists, thus, missing to find the
>> level-7 trap.
>> This is very hard to solve even if you have unlimited power.
>>
>> The plain MCTS as used by AlphaZero is the most ill-suited MCTS version
>> in my opinion and i have hard a hard time seeing how it can be competitive
>> with Stockfish tactically.
>>
>> My MCTS chess engine with  AlphaZero like MCTS was averaging was missing
>> a lot of tactics. I don't use policy or eval networks but qsearch() for
>> eval, and the policy is basically
>> choosing which ever moves leads to a higher eval.
>>
>> a) My first improvement to the MCTS is to use minimax backups instead of
>> averaging. This was an improvmenet but not something that would solve the
>> traps
>>
>> b) My second improvment is to use alphabeta rollouts. This is a rollouts
>> version that can do nullmove and LMR etc... This is a huge improvment and
>> none of the MCTS
>> versons can match it. More on alpha-beta rollouts here (
>> https://www.microsoft.com/en-us/research/wp-content/upload
>> s/2014/11/huang_rollout.pdf )
>>
>> So AlphaZero used none of the above improvements and yet it seems to be
>> tactically strong. Leela-Zero suffered from tactical falls left and right
>> too as I expected.
>>
>> So the only explanation left is the policy network able to avoid traps
>> which I find hard to believe it can identify more than a qsearch level
>> tactics.
>>
>> All I am saying is that my experience (as well as many others) with MCTS
>> for tactical dominated games is bad, and there must be some breakthrough in
>> that regard in AlphaZero
>> for it to be able to compete with Stockfish on a tactical level.
>>
>> I am curious how Remi's attempt at Shogi using AlphaZero's method will
>> turnout.
>>
>> regards,
>> Daniel
>>
>>
>>
>>
>>
>>
>>
>>
>> On Tue, Mar 6, 2018 at 9:41 AM, Brian Sheppard via Computer-go <
>> computer-go at computer-go.org> wrote:
>>
>>> Training on Stockfish games is guaranteed to produce a blunder-fest,
>>> because there are no blunders in the training set and therefore the policy
>>> network never learns how to refute blunders.
>>>
>>>
>>>
>>> This is not a flaw in MCTS, but rather in the policy network. MCTS will
>>> eventually search every move infinitely often, producing asymptotically
>>> optimal play. But if the policy network does not provide the guidance
>>> necessary to rapidly refute the blunders that occur in the search, then
>>> convergence of MCTS to optimal play will be very slow.
>>>
>>>
>>>
>>> It is necessary for the network to train on self-play games using MCTS.
>>> For instance, the AGZ approach samples next states during training games by
>>> sampling from the distribution of visits in the search. Specifically: not
>>> by choosing the most-visited play!
>>>
>>>
>>>
>>> You see how this policy trains both search and evaluation to be
>>> internally consistent? The policy head is trained to refute the bad moves
>>> that will come up in search, and the value head is trained to the value
>>> observed by the full tree.
>>>
>>>
>>>
>>> *From:* Computer-go [mailto:computer-go-bounces at computer-go.org] *On
>>> Behalf Of *Dan
>>> *Sent:* Monday, March 5, 2018 4:55 AM
>>> *To:* computer-go at computer-go.org
>>> *Subject:* Re: [Computer-go] 9x9 is last frontier?
>>>
>>>
>>>
>>> Actually prior to this it was trained with hundreds of thousands of
>>> stockfish games and didn’t do well on tactics (the games were actually a
>>> blunder fest). I believe this is a problem of the MCTS used and not due to
>>> for lack of training.
>>>
>>>
>>>
>>> Go is a strategic game so that is different from chess that is full of
>>> traps.
>>>
>>> I m not surprised Lela zero did well in go.
>>>
>>>
>>>
>>> On Mon, Mar 5, 2018 at 2:16 AM Gian-Carlo Pascutto <gcp at sjeng.org>
>>> wrote:
>>>
>>> On 02-03-18 17:07, Dan wrote:
>>> > Leela-chess is not performing well enough
>>>
>>> I don't understand how one can say that given that they started with the
>>> random network last week only and a few clients. Of course it's bad!
>>> That doesn't say anything about the approach.
>>>
>>> Leela Zero has gotten strong but it has been learning for *months* with
>>> ~400 people. It also took a while to get to 30 kyu.
>>>
>>> --
>>> GCP
>>> _______________________________________________
>>> Computer-go mailing list
>>> Computer-go at computer-go.org
>>> http://computer-go.org/mailman/listinfo/computer-go
>>>
>>>
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>>>
>>
>>
>
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