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Kimon Fountoulakis

@kfountou.bsky.social
1.1K followers 87 following 149 posts

Associate Professor at CS UWaterloo Machine Learning Lab: opallab.ca

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Kimon Fountoulakis @kfountou.bsky.social · 22/10/2025
I mean, it makes sense. If sky-net rules over everything, then Prince Harry will not be prince anymore.
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Kimon Fountoulakis @kfountou.bsky.social · 19/10/2025
Yes
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Kimon Fountoulakis @kfountou.bsky.social · 18/10/2025
3. This allows us to compute the eigenvalues of the Fourier transform exactly, and hence its spectral norm. Furthermore, we show that the mixing time of the random walk for our family is tight.
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Kimon Fountoulakis @kfountou.bsky.social · 18/10/2025
2. Remarkably, this Fourier transform is governed entirely by the standard representation of the group. Using tools from group and representation theory, the entire analysis collapses to that single representation.
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Kimon Fountoulakis @kfountou.bsky.social · 18/10/2025
Main proof technique. We couple two machines from this family as a random walk on the group S_n x S_n and show that, with high probability, they are indistinguishable. How? 1. Indistinguishability is controlled by the spectral norm of the Fourier transform of the walk’s single-step distribution.
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Kimon Fountoulakis @kfountou.bsky.social · 18/10/2025
We construct a large randomized family of shuffling machines. Each machine shuffles its input using only transpositions. By flipping a random coin to decide whether to apply or ignore each transposition, we obtain a randomized family with the desired properties.
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Kimon Fountoulakis @kfountou.bsky.social · 18/10/2025
We show that SQ hardness can be established when both the alphabet size and input length are polynomial in the number of states.
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Kimon Fountoulakis @kfountou.bsky.social · 18/10/2025
We prove the first SQ hardness result for learning semiautomata under the uniform distribution over input words and initial states, without relying on parity gadgets or adversarial inputs. The hardness is structural, it arises purely from the transition structure, not from hard languages.
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Kimon Fountoulakis @kfountou.bsky.social · 18/10/2025
On the Statistical Query Complexity of Learning Semiautomata: a Random Walk Approach Link to the paper: arxiv.org/abs/2510.04115
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Kimon Fountoulakis @kfountou.bsky.social · 09/06/2025
Done.
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Kimon Fountoulakis @kfountou.bsky.social · 27/05/2025
I wrote a blog post about it. Link: medium.com/@kimon.fount...
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Kimon Fountoulakis @kfountou.bsky.social · 27/05/2025
2) Can a neural network discover instructions for performing multiplication itself? The answer to the first question is yes, with high probability and up to some arbitrary, predetermined precision (see the quoted post).
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Kimon Fountoulakis @kfountou.bsky.social · 26/05/2025
Link to the paper: arxiv.org/abs/2502.16763 Link to the repository: github.com/opallab/bina...
arxiv.org
Learning to Add, Multiply, and Execute Algorithmic Instructions Exactly with Neural Networks
Neural networks are known for their ability to approximate smooth functions, yet they fail to generalize perfectly to unseen inputs when trained on discrete operations. Such operations lie at the hear...
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Kimon Fountoulakis @kfountou.bsky.social · 26/05/2025
Learning to execute arithmetic exactly, with high probability, can be quite expensive. In the plot, 'ensemble complexity' refers to the number of independently trained models required to achieve exact learning with high probability. ell is the number of bits per number in the input.
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Kimon Fountoulakis @kfountou.bsky.social · 26/05/2025
New paper: Learning to Add, Multiply, and Execute Algorithmic Instructions Exactly with Neural Networks
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Kimon Fountoulakis @kfountou.bsky.social · 26/05/2025
Learning to execute arithmetic exactly, with high probability, can be quite expensive. In the plot, 'ensemble complexity' refers to the number of independently trained models required to achieve exact learning with high probability. ell is the number of bits per number in the input.
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Kimon Fountoulakis @kfountou.bsky.social · 21/05/2025
I never understood the point of trams. They're slow and expensive. I've been to two cities that built them while I was there, Edinburgh and Athens, and in both cases, the projects were born out of corruption. Especially in Edinburgh, it was a disaster. en.wikipedia.org/wiki/Edinbur...
en.wikipedia.org
Edinburgh Tram Inquiry - Wikipedia
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Kimon Fountoulakis @kfountou.bsky.social · 17/05/2025
Thanks, the connection to formal languages is quite interesting. I have a section in the repo regarding formal languages but it's small mainly because it's not a topic that I am familiar with. I will add them!
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Kimon Fountoulakis @kfountou.bsky.social · 16/05/2025
Update, 14 empirical papers added!
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Kimon Fountoulakis @kfountou.bsky.social · 15/05/2025
The SIAM Conference on Optimization 2026 will be in Edinburgh! I don’t really work on optimization anymore (at least not directly), but it’s cool to see a major optimization conference taking place where I did my PhD.
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Kimon Fountoulakis @kfountou.bsky.social · 11/05/2025
Currently NeurIPS has 21390 submissions. The final number last year was 15671. Observation made by my student George Giapitzakis.
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Kimon Fountoulakis @kfountou.bsky.social · 07/05/2025
Got a pin this morning Einstein problem: en.wikipedia.org/wiki/Einstei...
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Reposted by Kimon Fountoulakis
Jason Lee @jasondeanlee.bsky.social · 05/05/2025
Our new work on scaling laws that includes compute, model size, and number of samples. The analysis involves an extremely fine-grained analysis of online sgd built up over the last 8 years of understanding sgd on simple toy models (tensors, single index models, multi index model)
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Kimon Fountoulakis @kfountou.bsky.social · 01/05/2025
Hey, I definitely predicted this correctly.
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Kimon Fountoulakis @kfountou.bsky.social · 01/05/2025
ChatGPT gives me the ability to expand my search capabilities on topics that I can only roughly describe, or even illustrate with a figure, when I don’t know the exact keywords to use in a Google search.
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Kimon Fountoulakis @kfountou.bsky.social · 01/05/2025
That's a comprehensive study on the expressivity for parallel algorithms, their in- and out-of-distribution learnability, and it includes a lot of experiments. link: arxiv.org/abs/2410.01686
arxiv.org
Positional Attention: Expressivity and Learnability of Algorithmic Computation
There is a growing interest in the ability of neural networks to execute algorithmic tasks (e.g., arithmetic, summary statistics, and sorting). The goal of this work is to better understand the role o...
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Kimon Fountoulakis @kfountou.bsky.social · 01/05/2025
Positional Attention is accepted at ICML 2025! Thanks to all co-authors for the hard work (64 pages). If you’d like to read the paper, check the quoted post.
arxiv.org
Positional Attention: Expressivity and Learnability of Algorithmic Computation
There is a growing interest in the ability of neural networks to execute algorithmic tasks (e.g., arithmetic, summary statistics, and sorting). The goal of this work is to better understand the role o...
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Kimon Fountoulakis @kfountou.bsky.social · 29/04/2025
NeurIPS 2026 in the Cyclades. Just saying.
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Kimon Fountoulakis @kfountou.bsky.social · 28/04/2025
Wait, isn't that America?
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Kimon Fountoulakis @kfountou.bsky.social · 27/04/2025
This is different from simply replacing the discontinuous activation in the neural network with a continuous one and then using standard NTK. link: openreview.net/forum?id=kfd...
openreview.net
A generalized neural tangent kernel for surrogate gradient learning
State-of-the-art neural network training methods depend on the gradient of the network function. Therefore, they cannot be applied to networks whose activation functions do not have useful...
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Kimon Fountoulakis @kfountou.bsky.social · 27/04/2025
They analyze a modified gradient flow, where the Jacobian for the training data uses an approximate derivative of the activation function.
openreview.net
A generalized neural tangent kernel for surrogate gradient learning
State-of-the-art neural network training methods depend on the gradient of the network function. Therefore, they cannot be applied to networks whose activation functions do not have useful...
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Kimon Fountoulakis @kfountou.bsky.social · 27/04/2025
I enjoyed reading the paper "A Generalized Neural Tangent Kernel for Surrogate Gradient Learning" (Spotlight, NeurIPS 2024). They extend the NTK framework to activation functions that have finitely many jumps.
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Reposted by Kimon Fountoulakis
Waterloo's David R. Cheriton School of Computer Science @uwcheritoncs.bsky.social · 24/04/2025
✍️ Code Shaping, an AI-powered software, allows users to edit their code through sketches like diagrams and graphs 📈 🏆 This game-changing platform won the Best Paper Award at #CHI2025. 🔗Read more: uwaterloo.ca/computer-sci... #UWaterloo #AI
uwaterloo.ca
New AI model turns sketches into code | Cheriton School of Computer Science | University of Waterloo
Co-developed by alum Ryan Yen, Code Shaping can transform coding beyond the keyboard.
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Kimon Fountoulakis @kfountou.bsky.social · 23/04/2025
Regarding this particular case, I can read exactly what the code is doing and it seems quite interpretable. I don't have to know some other library to understand the code. It seems to only use basic instructions.
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Kimon Fountoulakis @kfountou.bsky.social · 23/04/2025
I prefer more verbose coding, but again, I am only doing prototyping. I find it very annoying when someone's code includes efficient shortcuts that are hard to interpret without a lot of experience.
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Kimon Fountoulakis @kfountou.bsky.social · 23/04/2025
To be honest, I find the code by the chat way more readable, exactly because it's verbose. But, I suck at coding, I only prototype ideas...
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Reposted by Kimon Fountoulakis
Aleksandros Sobczyk @asobczyk.bsky.social · 14/04/2025
With my first Bluesky post, I am very pleased to share that my last PhD paper "Deterministic complexity analysis of Hermitian eigenproblems" has been accepted in ICALP 2025. A preprint is available on Arxiv: arxiv.org/abs/2410.21550 A bit more info on linkedin: www.linkedin.com/posts/aleksa...
arxiv.org
Deterministic complexity analysis of Hermitian eigenproblems
In this work we revisit the arithmetic and bit complexity of Hermitian eigenproblems. We first provide an analysis for the divide-and-conquer tridiagonal eigensolver of Gu and Eisenstat [GE95] in the ...
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Kimon Fountoulakis @kfountou.bsky.social · 13/04/2025
Update "Memory Augmented Large Language Models are Computationally Universal", Dale Schuurmans link: arxiv.org/abs/2301.04589
arxiv.org
Memory Augmented Large Language Models are Computationally Universal
We show that transformer-based large language models are computationally universal when augmented with an external memory. Any deterministic language model that conditions on strings of bounded length...
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Reposted by Kimon Fountoulakis
Alex Dimakis @alexdimakis.bsky.social · 13/04/2025
Excited to be part of Greeksin.ai
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Kimon Fountoulakis @kfountou.bsky.social · 12/04/2025
2) Weighted flow diffusion for local graph clustering with node attributes: an algorithm and statistical guarantees (ICML 2023, oral) 3) Local Hyper-flow Diffusion (NeurIPS 2021) 4) p-Norm Flow Diffusion for Local Graph Clustering (ICML 2020)
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Kimon Fountoulakis @kfountou.bsky.social · 12/04/2025
Shenghao's Ph.D Thesis "Perspectives of Graph Diffusion: Computation, Local Partitioning, Statistical Recovery, and Applications" is now available. Link: dspacemainprd01.lib.uwaterloo.ca/server/api/c... Relevant papers: 1) Local Graph Clustering with Noisy Labels (ICLR 2024)
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Kimon Fountoulakis @kfountou.bsky.social · 01/04/2025
I am still surprised by how difficult it is to train a 2-layer MLP to simply learn to copy or permute the input exactly. If k is the input length, the result below provides a (seemingly tight) upper bound of O(k²) training trials.
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Kimon Fountoulakis @kfountou.bsky.social · 31/03/2025
3. Neural Networks and the Chomsky Hierarchy. ICLR 2023. openreview.net/forum?id=Wbx... 4. Training Neural Networks as Recognizers of Formal Languages. ICLR 2025. openreview.net/forum?id=aWL...
openreview.net
Neural Networks and the Chomsky Hierarchy
Large-scale empirical study to determine the computational complexity class of a number of neural network architectures, which allows forecasting limitations on generalization capabilities.
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Kimon Fountoulakis @kfountou.bsky.social · 31/03/2025
New additions 1. Graph neural networks extrapolate out-of-distribution for shortest paths. arxiv.org/abs/2503.19173 2. Round and Round We Go! What makes Rotary Positional Encodings useful?. ICLR 2025. openreview.net/forum?id=Gtv...
arxiv.org
Graph neural networks extrapolate out-of-distribution for shortest paths
Neural networks (NNs), despite their success and wide adoption, still struggle to extrapolate out-of-distribution (OOD), i.e., to inputs that are not well-represented by their training dataset. Addres...
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Kimon Fountoulakis @kfountou.bsky.social · 23/03/2025
Our second kid arrived!
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Reposted by Kimon Fountoulakis
Max Thiessen @maxthiessen.bsky.social · 20/03/2025
GLOW is returning on 𝗠𝗮𝗿𝗰𝗵 𝟮𝟲𝘁𝗵, 𝟱𝗽𝗺 𝗖𝗘𝗧 with a special guest: @petar-v.bsky.social 🌟 He will lecture on LLMs as GNNs – a topic which received quite some attention at our last session. Specifically, we will learn how Graph ML tools can help understand LLM generalisation
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Kimon Fountoulakis @kfountou.bsky.social · 17/03/2025
1 out of 12 papers in my batch at ICML has a score above 3 (weak acceptance). Each paper has at least 3 reviews.
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Kimon Fountoulakis @kfountou.bsky.social · 11/03/2025
Exactly, score 1 does not distinguish bad papers from papers that have issues which can be solved. On the other hand, if both are in the rejection region, then from the perspective of the conference, it does not matter. I still think the previous scale was more accurate though.
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