Dmitry Vaintrob
Steelmanning heuristic arguments
I’m managing to get verve and probity, but having issues with wiles
I really liked the post—I was confused by the meaning and purpose no-coincidence principle when I was a ARC, and this post clarifies it well. I like that this is asking for something that is weaker than a proof (or a probabilistic weakening of proof), as [related to the example of using the Riemann hypothesis], in general you expect from incompleteness for there to be true results that lead to “surprising” families of circuits which are not provable by logic. I can also see Paul’s point of how this statement is sort of like P vs. BPP but not quite.
More specifically, this feels like a sort of 2nd-order boolean/polynomial hierarchy statement whose first-order version is P vs. BPP. Are there analogues of this for other orders?
Memorization-generalization in practice
Efficiency spectra and “bucket of circuits” cartoons
Looks like a conspiracy of pigeons posing as lw commenters have downvoted your post
The memorization-generalization spectrum and learning coefficients
Thanks!
I haven’t grokked your loss scales explanation (the “interpretability insights” section) without reading your other post though.
Not saying anything deep here. The point is just that you might have two cartoon pictures:
every correctly classified input is either the result of a memorizing circuit or of a single coherent generalizing circuit behavior. If you remove a single generalizing circuit, your accuracy will degrade additively.
a correctly classified input is the result of a “combined” circuit consisting of multiple parallel generalizing “subprocesses” giving independent predictions, and if you remove any of these subprocesses, your accuracy will degrade multiplicatively.
A lot of ML work only thinks about picture #1 (which is the natural picture to look at if you only have one generalizing circuit and every other circuit is a memorization). But the thing I’m saying is that picture #2 also occurs, and in some sense is “the info-theoretic default” (though both occur simultaneously—this is also related to the ideas in this post)
Thanks for the questions!
You first introduce the SLT argument that tells us which loss scale to choose (the “Watanabe scale”, derived from the Watanabe critical temperature).
Sorry, I think the context of the Watanabe scale is a bit confusing. I’m saying that in fact it’s the wrong scale to use as a “natural scale”. The Watanabe scale depends only on the number of training datapoints, and doesn’t notice any other properties of your NN or your phenomenon of interest.
Roughly, the Watanabe scale is the scale on which loss improves if you memorize a single datapoint (so memorizing improves accuracy by 1/n with n = #(training set) and in a suitable operationalization, improves loss by , and this is the Watanabe scale).
It’s used in SLT roughly because it’s the minimal temperature scale where “memorization doesn’t count as relevant”, and so relevant measurements become independent of the n-point sample. However in most interp experiments, the realistic loss reconstruction loss reconstruction is much rougher (i.e., further from optimal loss) than the 1/n scale where memorization becomes an issue (even if you conceptualize #(training set) as some small synthetic training set that you were running the experiment on).
For your second question: again, what I wrote is confusing and I really want to rewrite it more clearly later. I tried to clarify what I think you’re asking about in this shortform. Roughly, the point here is that to avoid having your results messed up by spurious behaviors, you might want to degrade as much as possible while still observing the effect of your experiment. The idea is that if you found any degradation that wasn’t explicitly designed with your experiment in mind (i.e., is natural), but where you see your experimental results hold, then you have “found a phenomenon”. The hope is that if you look at the roughest such scale, you might kill enough confounders and interactions to make your result be “clean” (or at least cleaner): so for example optimistically you might hope to explain all the loss of the degraded model at the degradation scale you chose (whereas at other scales, there are a bunch of other effects improving the loss on the dataset you’re looking at that you’re not capturing in the explanation).
The question now is when degrading, what order you want to “kill confounders” in to optimally purify the effect you’re considering. The “natural degradation” idea seems like a good place to look since it kills the “small but annoying” confounders: things like memorization, weird specific connotations of the test sentences you used for your experiment, etc. Another reasonable place to look is training checkpoints, as these correspond to killing “hard to learn” effects. Ideally you’d perform several kinds of degradation to “maximally purify” your effect. Here the “natural scales” (loss on the level Claude 1 e.g., or Bert) are much too fine for most modern experiments, and I’m envisioning something much rougher.
The intuition here comes from physics. Like if you want to study properties of a hydrogen atom that you don’t see either in water or in hydrogen gas, a natural thing to do is to heat up hydrogen gas to extreme temperatures where the molecules degrade but the atoms are still present, now in “pure” form. Of course not all phenomena can be purified in this way (some are confounded by effects both at higher and at lower temperature, etc.).
Thanks! Yes the temperature picture is the direction I’m going in. I had heard the term “rate distortion”, but didn’t realize the connection with this picture. Might have to change the language for my next post
My supervillain origin story
This seems overstated
In some sense this is the definition of the complexity of an ML algorithm; more precisely, the direct analog of complexity in information theory, which is the “entropy” or “Solomonoff complexity” measurement, is the free energy (I’m writing a distillation on this but it is a standard result). The relevant question then becomes whether the “SGLD” sampling techniques used in SLT for measuring the free energy (or technically its derivative) actually converge to reasonable values in polynomial time. This is checked pretty extensively in this paper for example.
A possibly more interesting question is whether notions of complexity in interpretations of programs agree with the inherent complexity as measured by free energy. The place I’m aware of where this is operationalized and checked is our project with Nina on modular addition: here we do have a clear understanding of the platonic complexity, and the local learning coefficient does a very good job of asymptotically capturing it with very good precision (both for memorizing and generalizing algorithms, where the complexity difference is very significant).
Citation? [for Apollo]
Look at this paper (note I haven’t read it yet). I think their LIB work is also promising (at least it separates circuits of small algorithms)
Thanks for the reference, and thanks for providing an informed point of view here. I would love to have more of a debate here, and would quite like being wrong as I like tropical geometry.
First, about your concrete question:
As I understand it, here the notion of “density of polygons’ is used as a kind of proxy for the derivative of a PL function?
Density is a proxy for the second derivative: indeed, the closer a function is to linear, the easier it is to approximate it by a linear function. I think a similar idea occurs in 3D graphics, in mesh optimization, where you can improve performance by reducing the number of cells in flatter domains (I don’t understand this field, but this is done in this paper according to some energy curvature-related energy functional). The question of “derivative change when crossing walls” seems similar. In general, glancing at the paper you sent, it looks like polyhedral currents are a locally polynomial PL generalization of currents of ordinary functions (and it seems that there is some interesting connection made to intersection theory/analogues of Chow theory, though I don’t have nearly enough background to read this part carefully). Since the purpose of PL functions in ML is to approximate some (approximately smooth, but fractally messy and stochastic) “true classification”, I don’t see why one wouldn’t just use ordinary currents here (currents on a PL manifold can be made sense of after smoothing, or in a distribution-valued sense, etc.).
In general, I think the central crux between us is whether or not this is true:
tropical geometry might be relevant ML, for the simple reason that the functions coming up in ML with ReLU activation are PL
I’m not sure I agree with this argument. The use of PL functions is by no means central to ML theory, and is an incidental aspect of early algorithms. The most efficient activation functions for most problems tend to not be ReLUs, though the question of activation functions is often somewhat moot due to the universal approximation theorem (and the fact that, in practice, at least for shallow NNs anything implementable by one reasonable activation tends to be easily implementable, with similar macroscopic properties, by any other). So the reason that PL functions come up is that they’re “good enough to approximate any function” (and also “asymptotic linearity” seems genuinely useful to avoid some explosion behaviors). But by the same token, you might expect people who think deeply about polynomial functions to be good at doing analysis because of the Stone-Weierstrass theorem.
More concretely, I think there are two core “type mismatches” between tropical geometry and the kinds of questions that appear in ML:
Algebraic geometry in general (including tropical geometry) isn’t good at dealing with deep compositions of functions, and especially approximate compositions.
(More specific to TG): the polytopes that appear in neural nets are as I explained inherently random (the typical interpretation we have of even combinatorial algorithms like modular addition is that the PL functions produce some random sharding of some polynomial function). This is a very strange thing to consider from the point of view of a tropical geometer: like as an algebraic geometer, it’s hard for me to imagine a case where “this polynomial has degree approximately 5… it might be 4 or 6, but the difference between them is small”. I simply can’t think of any behavior that is at all meaningful from an AG-like perspective where the questions of fan combinatorics and degrees of polynomials are replaced by questions of approximate equality.
I can see myself changing my view if I see some nontrivial concrete prediction or idea that tropical geometry can provide in this context. I think a “relaxed” form of this question (where I genuinely haven’t looked at the literature) is whether tropical geometry has ever been useful (either in proving something or at least in reconceptualizing something in an interesting way) in linear programming. I think if I see a convincing affirmative answer to this relaxed question, I would be a little more sympathetic here. However, the type signature here really does seem off to me.
The generalization phase diagram
On polytopes
QFT and neural nets: the basic idea
If I understand correctly, you want a way of thinking about a reference class of programs that has some specific, perhaps interpretability-relevant or compression-related properties in common with the deterministic program you’re studying?
I think in this case I’d actually say the tempered Bayesian posterior by itself isn’t enough, since even if you work locally in a basin, it might not preserve the specific features you want. In this case I’d probably still start with the tempered Bayesian posterior, but then also condition on the specific properties/explicit features/ etc. that you want to preserve. (I might be misunderstanding your comment though)
Thanks for this post. I would argue that part of an explanation here could also be economic: modernity brings specialization and a move from the artisan economy of objects as uncommon, expensive, multipurpose, and with a narrow user base (illuminated manuscripts, decorative furniture) to a more utilitarian and targeted economy. Early artisans need to compete for a small number of rich clients by being the most impressive, artistic, etc., whereas more modern suppliers follow more traditional laws of supply and demand and track more costs (cost-effectiveness, readability and reader’s time vs. beauty and remarkableness). And consumers similarly can decouple their needs: art as separate from furniture and architecture, poetry and drama as separate from information and literature. I think another aspect of this shift, that I’m sad we’ve lost, is the old multipurpose scientific/philosophical treatises with illustrations or poems (my favorite being de Rerum Natura, though you could argue that Nietzsche and Wagner tried to revive this with their attempts at Gesamtkunstwerke).