Chulhee "Charlie" Yun

Hi!

My name is Charlie, and I am a postdoctoral Research Specialist in the Laboratory for Information and Decision Systems at Massachusetts Institute of Technology. I recently finished my Ph.D. from the same laboratory. Hosted by my awesome Ph.D. advisors Prof. Ali Jadbabaie and Prof. Suvrit Sra, I work on optimization and machine learning. Before joining MIT, I was a master’s student in Electrical Engineering at Stanford University, where I had a great fortune to work with Prof. John Duchi. I finished my undergraduate program in Electrical Engineering at KAIST, South Korea.

I will be joining KAIST Graduate School of AI as an assistant professor starting in Spring 2022. I am looking for self-motivated students that are interested in theoretical aspects of optimization and machine learning. A strong background in mathematics and computer science would be a huge plus. Feel free to reach out to me if you are interested.

[Google Scholar]

Research Interests

  • Convergence analysis of without-replacement optimization algorithms
  • Algorithm trajectory analysis of optimization in deep learning
  • Explaining generalization in deep learning
  • Federated/distributed learning
  • Expressive power of neural networks
  • Optimization landscape of neural networks
  • Fundamental limits and lower bounds for optimization algorithms
  • … and any interesting topics in OPT/ML, including applications

Contact

News

[08/2021] After defending my Ph.D. in late July, I finally submitted my doctoral thesis!

[06/2021] Two publications to be presented at COLT 2021: “Provable Memorization via Deep Neural Networks using Sub-linear Parameters” (Main Track) and “Open Problem: Can Single-Shuffle SGD be Better than Reshuffling SGD and GD?” (Open Problems Track).

[06/2021] I decided to join KAIST Graduate School of AI as an assistant professor! 

[01/2021] Two papers accepted to ICLR 2021: “Minimum Width for Universal Approximation” (Spotlight) and “A Unifying View on Implicit Bias in Training Linear Neural Networks” (Poster).

[09/2020] Two papers got accepted to NeurIPS 2020: “SGD with shuffling: optimal rates without component convexity and large epoch requirements” (Spotlight) and “O(n) Connections are Expressive Enough: Universal Approximability of Sparse Transformers” (Poster).

[09/2020] Our results on the expressive power of deep and narrow networks (partly based on a recent preprint) are to be presented as a contributed talk at the DeepMath 2020 conference!

[06/2020] Started my second summer internship at Google Research, hosted by Hossein Mobahi and Shankar Krishnan.

[Older News]

Publications

* indicates alphabetical order or equal contribution.

Preprints

Minibatch vs Local SGD with Shuffling: Tight Convergence Bounds and Beyond [arXiv]
Chulhee Yun, Shashank Rajput, Suvrit Sra

Conference/Workshop Papers

Open Problem: Can Single-Shuffle SGD be Better than Reshuffling SGD and GD? [long version]
Chulhee Yun, Suvrit Sra, Ali Jadbabaie
Conference on Learning Theory (COLT) 2021

Provable Memorization via Deep Neural Networks using Sub-linear Parameters [arXiv]
Sejun Park, Jaeho Lee, Chulhee Yun, Jinwoo Shin
Conference on Learning Theory (COLT) 2021
Presented as a contributed talk at DeepMath 2020

A Unifying View on Implicit Bias in Training Linear Neural Networks [arXiv]
Chulhee Yun, Shankar Krishnan, Hossein Mobahi
International Conference on Learning Representations (ICLR) 2021
NeurIPS 2020 Workshop on Optimization for Machine Learning: OPT 2020

Minimum Width for Universal Approximation [arXiv]
Sejun Park, Chulhee Yun, Jaeho Lee, Jinwoo Shin
International Conference on Learning Representations (ICLR) 2021 (Spotlight)
Presented as a contributed talk at DeepMath 2020

SGD with shuffling: optimal rates without component convexity and large epoch requirements [arXiv]
Kwangjun Ahn*, Chulhee Yun*, Suvrit Sra
Neural Information Processing Systems (NeurIPS) 2020 (Spotlight)

O(n) Connections are Expressive Enough: Universal Approximability of Sparse Transformers [arXiv]
Chulhee Yun, Yin-Wen Chang, Srinadh Bhojanapalli, Ankit Singh Rawat, Sashank J. Reddi, Sanjiv Kumar
Neural Information Processing Systems (NeurIPS) 2020

Low-Rank Bottleneck in Multi-head Attention Models [arXiv]
Srinadh Bhojanapalli, Chulhee Yun, Ankit Singh Rawat, Sashank J. Reddi, Sanjiv Kumar
International Conference on Machine Learning (ICML) 2020

Are Transformers universal approximators of sequence-to-sequence functions? [arXiv] [paper] [slides]
Chulhee Yun, Srinadh Bhojanapalli, Ankit Singh Rawat, Sashank J. Reddi, Sanjiv Kumar
International Conference on Learning Representations (ICLR) 2020
NeurIPS 2019 Workshop on Machine Learning with Guarantees [short paper] [poster]
NYAS Machine Learning Symposium 2020 Poster Awards – Honorable Mention

Are deep ResNets provably better than linear predictors? [arXiv] [paper] [slides] [poster]
Chulhee Yun, Suvrit Sra, Ali Jadbabaie
Neural Information Processing Systems (NeurIPS) 2019

Small ReLU networks are powerful memorizers: a tight analysis of memorization capacity [arXiv] [paper] [slides] [poster]
Chulhee Yun, Suvrit Sra, Ali Jadbabaie
Neural Information Processing Systems (NeurIPS) 2019 (Spotlight)

Efficiently testing local optimality and escaping saddles for ReLU networks [arXiv] [paper]
Chulhee Yun, Suvrit Sra, Ali Jadbabaie
International Conference on Learning Representations (ICLR) 2019

Small nonlinearities in activation functions create bad local minima in neural networks [arXiv] [paper]
Chulhee Yun, Suvrit Sra, Ali Jadbabaie
International Conference on Learning Representations (ICLR) 2019

Minimax Bounds on Stochastic Batched Convex Optimization [paper]
John Duchi*, Feng Ruan*, Chulhee Yun*
Conference on Learning Theory (COLT) 2018

Global optimality conditions for deep neural networks [arXiv] [paper]
Chulhee Yun, Suvrit Sra, Ali Jadbabaie
International Conference on Learning Representations (ICLR) 2018
NIPS 2017 Workshop on Deep Learning: Bridging Theory and Practice [short paper]

Face detection using local hybrid patterns [paper]
Chulhee Yun, Donghoon Lee, Chang D. Yoo
International Conference on Acoustics, Speech and Signal Processing (ICASSP) 2015

Talks

  • Open Problem: Can Single-Shuffle SGD be Better than Reshuffling SGD and GD? COLT 2021 Open Problem Talk. Aug 2021.
  • A Unifying View on Implicit Bias in Training Linear Neural Networks. ICLR 2021 Social: ML in Korea. May 2021.
  • Towards Bridging Theory and Practice in Deep Learning & Optimization. Google PhD Tech Talk. Apr 2021.
  • Bridging Theory and Practice in Deep Learning & Optimization. KAIST Graduate School of AI Special Seminar. Apr 2021.
  • Bridging Theory and Practice in Deep Learning & Optimization. POSTECH Computer Science and Engineering & Graduate School of AI Special Seminar. Apr 2021.
  • Implicit bias in neural network optimization: a unifying approach. KAIST Stochastic Analysis & Application Research Center AI Seminar. Apr 2021.
  • SGD with shuffling: optimal rates without component convexity and large epoch requirements. NeurIPS 2020 Spotlight Talk. Dec 2020.
  • SGD with shuffling: optimal convergence rates and more. SNU CSE Seminar. Dec 2020.
  • Theory of optimization in deep learning. KAIST Graduate School of AI Fall 2020 Colloquium. Oct 2020.
  • On the optimality and memorization in deep learning. Invited Talk at Harvard CRISP Group Meeting. Mar 2020.
  • Small ReLU networks are powerful memorizers: a tight analysis of memorization capacity. The 25th LIDS Student Conference. Jan 2020.
  • Small ReLU networks are powerful memorizers: a tight analysis of memorization capacity. NeurIPS 2019 Spotlight Talk. Dec 2019. [slides]
  • On the Global and Local Optimality of Deep Learning. KAIST ISysE Seminar. Feb 2019.
  • Small nonlinearities in activation functions create bad local minima in neural networks. The 24th LIDS Student Conference. Feb 2019.
  • Spurious Local Minima in Neural Networks: A Critical View. The 2018 INFORMS Annual Meeting. Nov 2018.
  • Global optimality conditions for deep linear neural networks. The 23rd LIDS Student Conference. Feb 2018. [slides]

Awards

Gratefully, my study has been supported by numerous scholarships and awards. To name a few:

Services

  • Reviewer/Program Committee: ICLR 2019–22, ICML 2019–21, COLT 2020–21, NeurIPS 2018–20, AISTATS 2019, CDC 2018, JMLR, SIAM Journal on Mathematics of Data Science, Annals of Statistics, IEEE TNNLR, IEEE Transactions on Information Theory
  • Co-Organizer: The 24th Annual LIDS Student Conference 2019
  • Co-Organizer: The LIDS & Stats Tea Talk Series, Fall 2019–Spring 2020

Last update: 8/31/2021