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Alpha Go Zero: How and Why It Works

tim.hibal.org

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Re: Alpha Go Zero: How and Why It Works

#41
post #33

If the author's here: some of the math formulas don't render correctly. In particular, 10^170 is parsed as 10^{1}70, and $5478$ shows up without TeX applied to it.

Thanks, fixed those

Another minor fix:

> A new paper was released a few days detailing a new neural net

I believe you mean "a few days ago"?

Re: Alpha Go Zero: How and Why It Works

#42

Mageek, any reason why they haven't applied this to chess yet?

MCTS has done very poorly on chess compared to alpha-beta. Chess has a high number of forcing moves in capture sequences, and it's been very difficult to evaluate positions that are not settled. Traditionally an algorithm called a quiescence search is used, but it relies on doing an evaluation at each node of the search, which would be prohibitive with the latency for a network evaluation.

One of the things that amazed me the most about AlphaGo Zero was that they didn't do any tricks to minimize the latency of the network evaluation!

Still, it's certainly worth a try, I'd be extremely interested to see what style of chess a self-trained MCTS chess version would have :).

Re: Alpha Go Zero: How and Why It Works

#43
post #26

The main reason AlphaGo Zero learns so much faster than its predecessors is because it uses temporal-difference learning.[1] This effectively removes a huge amount of the value network's state space for the learning algorithm to search through, since it bakes in the assumption that a move's value ought to equal that of the best available move in the following board position, which is exactly what you'd expect for a g…

Interestingly, the idea behind temporal difference learning is more or less the intuition behind how people price derivatives in finance.

The expected value of a contract at time T, estimated at some time t expected estimate, made n months from now, of the value [12-n] months later, will also be $100. This allows you to shrink the state space considerably.

You can usually work out the payoff of a derivatives in different scenarios given rational exercise decisions by all contract participants. The calculation assumes that every market participant makes the best possible decision given the information they had available at the time by either explicitly or implicitly building a tree and working backwards, back-propagating the 'future' value back to the root.

This closely resembles the modeling of a discrete adversarial game, except the payoffs need to make reference to random market variables like the stock price, so the tree nodes are not just indexed by participant action, but also by variables.

There's actually a nice resemblance between the Longstaff-Schwarz method of pricing American options and MCTS + Alphago, except that the former is using kernel regressions instead of deep neural nets and we sample from a continuous space with an assumed probability distribution instead of a discrete space guided by a policy network [1].

[1] https://people.math.ethz.ch/~hjfurrer/teaching/LongstaffSchw...

Re: Alpha Go Zero: How and Why It Works

#44

Earlier quoted context omitted.

What do you mean? AlphaGo Zero has played itself, and they have published 20 of those games.

the OP is referring to the use of a GAN, which is a different type of setup. GAN's were not used for alphaGo, as the article points out Deepmind uses reinforcement learning and MCTS.

They're most likely referring to adversarial attacks where degenerate inputs are constructed that could cause AlphaGo Zero to perform sub-optimally or catastrophically fail (see OpenAI Research [0]). This is distinct from generative adversarial networks (GANs) or adversarial self-play (which I guess AlphaGo Zero is an example of).

[0] https://blog.openai.com/adversarial-example-research/

Re: Alpha Go Zero: How and Why It Works

#46
Saw the AlphaGo movie at a festival recently.

Been following the AlphaGo Zero developments, which leap-frog what was going on in the movie (although still very much worth seeing).

One thing I was curious about is if Go would be considered solved, either hard or weakly solved, since AlphaGo Zero at this point doesn't seem to be able to be beat by any living human. Wikipedia does not list it as solved in either sense, and I was wondering if this was an oversight.

Re: Alpha Go Zero: How and Why It Works

#47
post #46

Saw the AlphaGo movie at a festival recently. Been following the AlphaGo Zero developments, which leap-frog what was going on in the movie (although still very much worth seeing). One thing I was curious about is if Go would be considered solved, either hard or weakly solved, since AlphaGo Zero at this point doesn't seem to be able to be beat by any living human. Wikipedia does not list it as solved in either sense,…

if alpha go is just an adversarial network to brute force states, then it is not solved (note I don't research alphaGo, and most of what I know about it is from HN comments)

Re: Alpha Go Zero: How and Why It Works

#48
post #4
post #2

I wonder how the STYLE of Alpha Go Zero is regarded by human experts. Is it far different from AlphaGo? Why bother learning from AlphaGo if they can learn from AlphaGo Zero? Did they unleash a second "Master" program? I am wondering if the "better" strategy moves are now super wacky and weird and break all theory.

At least initial reports are that alphaGo Zero is more human-like than Master. Zero packs even more of the inhuman ability to pick the most critical part of the board for each move, but less weird looking stuff. In fact, one of the obvious differences between AlphaGo Zero and top human players, is much more play on safe opening spots, which has been out of fashion among human pros for a hundred years or so.

>At least initial reports are that alphaGo Zero is more human-like than Master.

Empirically, this is not correct. The original AlphaGo achieved a 57% accuracy at predicting expert moves.

I can't find an exact number, but based on the graph in the nature article, AlphaGo Zero has a less than 50% accuracy at predicting human moves. Eyeballing the graph, it looks like the supervized learning variant of AlphaGo Zero scored Of course, it is not clear that ability to predict the move humans will play is the best metric to measure how human like a computer plays. It is just the only objective metric we have. Although, if this were an actual research question, we could probably come up with better metrics.

https://storage.googleapis.com/deepmind-media/alphago/AlphaG...

https://www.nature.com/nature/journal/v550/n7676/pdf/nature2...

Re: Alpha Go Zero: How and Why It Works

#49
post #26

The main reason AlphaGo Zero learns so much faster than its predecessors is because it uses temporal-difference learning.[1] This effectively removes a huge amount of the value network's state space for the learning algorithm to search through, since it bakes in the assumption that a move's value ought to equal that of the best available move in the following board position, which is exactly what you'd expect for a g…

Interestingly, the idea behind temporal difference learning is more or less the intuition behind how people price derivatives in finance. The expected value of a contract at time T, estimated at some time t expected estimate, made n months from now, of the value [12-n] months later, will also be $100 . This allows you to shrink the state space considerably. You can usually work out the payoff of a derivatives in diff…

I think the bellman equation (which is used extensively in reinforcement learning) is also taught in stochastic calculus for finance (except in the continuous form?). https://en.wikipedia.org/wiki/Hamilton%E2%80%93Jacobi%E2%80%...

My memory is hazy so there might not be a real connection here.

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