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An exact mapping between the Variational Renormalization Group and Deep Learning

Pankaj Mehta, David J. Schwab

2014 · arXiv

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From the abstract

Deep learning is a broad set of techniques that uses multiple layers of representation to automatically learn relevant features directly from structured data. Recently, such techniques have yielded record-breaking results on a diverse set of difficult machine learning tasks in computer vision, speech recognition, and natural language processing. Despite the enormous success of deep learning, relatively little is understood theoretically about why these techniques are so successful at feature learning and compression. Here, we show that deep learning is intimately related to one of the most important and successful techniques in theoretical physics, the renormalization group (RG). RG is an iterative coarse-graining scheme that allows for the extraction of relevant features (i.e. operators) as a physical system is examined at different length scales. We construct an exact mapping from the variational renormalization group, first introduced by Kadanoff, and deep learning architectures based on Restricted Boltzmann Machines (RBMs). We illustrate these ideas using the nearest-neighbor Ising Model in one and two-dimensions. Our results suggests that deep learning algorithms may be employing a generalized RG-like scheme to learn relevant features from data.

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9 selected excerpts · 9 total mentions

riemannzeta
Recommendation · rule
Thanks for this additional link, which really underscores for me at least how you're right about patterns in circuits being a better abstraction layer for capturing interesting patterns than topological manifolds. I wasn't familiar with the term "equivariance" but I "woke up" to this sort of approach to understanding deep neural networks when I read this paper, which shows how restricted boltzman machines have an exact mapping to the renormalization group approach used to study phase transitions in condensed matter and high energy physics: https://arxiv.org/abs/1410.3831 At high enough energy, everything is symmetric. As energy begins to drain from the system, eventually every symmetry is broken. All fine structure emerges from the breaking of some symmetries. I'd love to get more in the weeds on this work. I'm in my own local equilibrium of sorts doing much more mundane stuff.
mlevental
Neutral mention · rule
it's quite plausible that at the fringe/edge there is research being done that involves differential geometry - hell there's this paper https://arxiv.org/pdf/1410.3831v1.pdf that's occupies very rarefied air, but that's not what the person to whom i'm responding to claims (that somewhere someone there's a relationship): >DG is the foundation of all modern AI/ML/DL which is just blather spoken in a tone of confidence in order to sound very smart.
cs702
Neutral mention · rule
Thank you for posting this. Similar thoughts have been percolating in my stream-of-consciousness for a while, especially after coming across an earlier version of Tegmark & Lin's paper some months ago. My take is that deep neural nets work so well in practice because not all distributions of natural data are equally likely (and therefore, the no-free-lunch theorem(s), which assumes all distributions are equally likely, doesn't hold in the real world!); and that, in turn, is because the distribution of natural data is a consequence of the laws of Physics / symmetries of the universe in which we happen to live. PS. You will enjoy the following papers too: "An exact mapping between the Variational Renormalization Group and Deep Learning" - https://arxiv.org/abs/1410.3831 ; and "Mutual Information, Neural Networks and the Renormalization Group" - https://arxiv.org/abs/1704.06279 .
epberry
Neutral mention · rule
Part of me says that you are correct on all of these points. However I think you went too far on 3. Experimentation does not always follow theory in science. I would argue that many of the great discoveries of physics in the 20th century followed directly from startling results of experiments conducted at the end of the 19th century (the photoelectric effect for example). I agree that there seems to be an awful lot of experimenting going on and that hardware and large datasets have helped tremendously but there are also many researchers poking and prodding at deep learning theory [1, 2]. So from a glass-half-full perspective we have rapid (sometimes iterative) experimentation coupled with yawning gaps in theory to explain surprising results. In other words, the opposite of previous AI booms and a big reason to be optimistic despite all the hype. [1] https://arxiv.org/pdf/1410.3831v1.pdf [2] https://arxiv.org/abs/1608.08225
ssivark
Neutral mention · rule
I am working on a project (using Julia) to "learn" an efficient representation of scale invariant many-body quantum states from a microscopic Hamiltonian. The particular structure being learned is supposed to be highly efficient both in representational complexity and computational complexity for predicting physical observables. (Work in progress at https://github.com/sivark/jumera/ ) Also reading/thinking about ideas at the heart of theoretical physics and machine learning. In particular, I've spent the last several months in trying to understand the following two papers in increasing levels of depth 1. https://arxiv.org/abs/1410.3831 2. https://arxiv.org/abs/1503.02406
adityab
Neutral mention · rule
You should watch Max Tegmark's talk "Connections between Physics and Deep Learning" if this interests you [1]. Additionally, a paper that has everyone excited about deep connections between the mathematical analysis of physical systems and the hierarchical feature learning paradigm speaks of the connection in terms of the Renormalization Group [2]. Regardless of it's practical utility, the philosophical implications do tickle the intellect. On a dreamy note, I wonder if it would be possible to draw Category-theoretic parallels between some physical theories and statistical learning theory. There is so much to learn, and I am trying my best to teach myself (on the side) the mathematics that they don't teach in my CS grad school. So much to learn, such little time. :) [1] https://youtu.be/5MdSE-N0bxs [2] http://arxiv.org/abs/1410.3831
T-A
Neutral mention · rule
To establish in a semi-rigorous way the (btw obvious) relationship between coarsening in physics and in stacked neural networks, as was done long after the latter became a thing [1][2], is at the same level as observing the analogy between Black-Scholes and diffusion. It's cute, but it does not turn the subject into physics. It should go without saying that you can not, by definition, resolve fundamental questions about mathematical physics by experiment. The APS took a stand on climate change years ago [3]. It was clear enough to make Harold Lewis [4] and Ivar Glaever [5] resign in protest. P.S. Belief propagation was first proposed by Judea Pearl in 1982 [6]. The…
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closest connection to physics one could realistically claim is that Pearl got a M.Sc. in physics before turning (back) to electrical engineering and then AI. [1] http://arxiv.org/abs/1301.3124 [2] http://arxiv.org/abs/1410.3831 [3] http://www.aps.org/policy/statements/climate/ [4] http://dotearth.blogs.nytimes.com/2010/10/15/a-physicists-cl... [5] http://www.telegraph.co.uk/news/earth/environment/climatecha... [6] https://www.aaai.org/Papers/AAAI/1982/AAAI82-032.pdf
thisisdave
Neutral mention · rule
This could be an important result, since there's a lot of theory and expertise regarding renormalization group methods, but I think it's too early to tell. The write-up is a bit misleading, though: the model in their preprint[1] is about stacks of restricted Boltzmann machines (RBMs), and are very different from the other examples of deep learning mentioned. The Google Cat Detector model, for example, didn't describe a probability distribution over images, which is the kind of task that the preprint is about. And in almost all of the recent cases where deep neural networks have made substantial progress over the previous state of the art, the models have not been…
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probabilistic, or trained layer-by-layer, or unsupervised, like the RBM-based approach in the preprint. I don't speak physics, but my reading of the paper says that could be summarized pretty accurately as follows: 1. Hinton et al. (2006) showed that each layer in a stack of RBMs improves a variational lower bound on p(x). 2. Variational methods for RG also iteratively improve a variational lower bound on p(x). 3. The two methods would thus be equivalent, if we could fit them without error (which we can't). 4. Here’s a figure from a stack of RBMs that vaguely looks like RG results (not shown) I don't see any comparison between the approximations that physicists normally use versus the contrastive divergence for training RBM-based networks, or evidence that their results are more similar in practice than any other technique. Am I missing something? [1] http://arxiv.org/abs/1410.3831 [2] https://www.cs.toronto.edu/~hinton/absps/fastnc.pdf
riemannzeta
Neutral mention · rule
Love this curious and open-minded exploration of how this stuff works. The pyramid strategy loosely tracks with renormalization group theory, which has been formally studied for years as a method of interpreting machine learning models: https://arxiv.org/abs/1410.3831 I love the convergence we're seeing in the use of models from different fields to understand machine learning, fundamental physics, and human consciousness. What a time to be alive.

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