I've had the fortune of participating in a diverse range of interesting research projects with great mentors and company.
Lazy Abstraction-Based Control for Reachability
preprint, under review for IEEE Transactions on Automatic Control (TAC)
project page /
In prior work, we introduced lazy abstraction-based controller synthesis (ABCS), but only for safety specifications.
Extending lazy ABCS to handle reachability specifications requires carefully maintaining a set of frontier states from the current progress of synthesis.
These frontier states are defined by their proximity to the domain of the controller.
After computing the abstract transitions for frontier states, we enable synthesis to make further progress.
We carefully restrict the progress synthesis can make in a single construct-then-synthesize iteration to avoid premature termination.
We empirically demonstrate performance benefts of lazy multi-layered ABCS over multi-layered ABCS.
Unsupervised Learning via Meta-Learning
International Conference on Learning Representations (ICLR), 2019
project page /
Unsupervised learning is commonly used as a pre-training step for downstream task learning.
However, the objective used during unsupervised learning is often agnostic to the downstream task type.
In this work, we propose CACTUs, an unsupervised learning algorithm that leverages meta-learning techniques to learn to learn tasks constructed from unlabeled data.
By incorporating knowledge of the downstream task type (image classification) into the unsupervised learning phase, CACTUs leads to significantly more effective downstream learning and enables few-shot learning without requiring labeled meta-learning datasets.
This kind of unsupervised meta-learning approach is especially appealing to instantiate for domains where meta-training tasks are cumbersome to specify.
Lazy Abstraction-Based Control for Safety Specifications
IEEE Conference on Decision and Control (CDC), 2018
project page /
There is a trade-off between single- and multi-layered abstraction based controller synthesis (ABCS): the latter speeds up synthesis, but requires more computation to construct the additional coarser abstractions.
This is because the abstract system computation is done in its entirety upfront, before synthesis begins.
In this work, we restrict our attention to safety specifications.
We extend multi-layered ABCS to be lazy: we entwine abstraction and synthesis to enable on-demand construction of the abstractions.
Instead of computing all the abstractions for the entire system, the algorithm selectively chooses which portions of the system to compute abstract transitions for, avoiding doing so for portions that have been already solved by synthesis.
This co-dependence of the two major components of ABCS is both conceptually appealing and results in significant performance benefits.
Multi-Layered Abstraction-Based Controller Synthesis for Continuous-Time Systems
Hybrid Systems: Computation and Control (HSCC), 2018
Abstraction-based controller synthesis (ABCS) is a class of techniques for correct-by-construction controller synthesis for nonlinear, perturbed, hybrid systems and linear temporal logic specifications.
First, a finite, discrete abstraction of the original system and specification is constructed.
Second, the abstract problem is solved using standard techniques from software verification.
Third, the abstract solution is refined into a controller for the original system.
Prior to this work, the procedure of ABCS was carried out in a single-layered setting; only one abstract system is constructed and used to find a controller.
This is computationally wasteful because bottleneck regions of the system dictate the resolution (and therefore computational burden) at which ABCS operates for the entire problem.
In this work, we generalize ABCS and present multi-layered ABCS: we construct multiple abstractions of the system at various spatiotemporal granularity, and do synthesis by adaptively switching between these layers, prioritizing the use of coarser, cheaper layers wherever possible, but leveraging the precision of finer, more expensive layers when necessary.
We prove soundness and completeness properties of our approach, and empirically verify that it is a first step towards scalable ABCS.
Germanium Wrap-Around Photodetectors on Silicon Photonics
Tae Joon Seok,
Ming C. Wu
Optics Express, 2015
We present a new photodetector architecture based on coupling the silicon waveguide and germanium diode by
wrapping the latter around the former instead of stacking them together. As a high school student,
I contributed by testing fabricated samples.
*Alphabetical authorship order.
Books I've Read
These are works that I consider particularly important to me, at least nostalgically. They are listed (roughly) in the order I read them, bottom-up. Some simply provided escapism. Many had a developmental impact on my worldview, introduced me to important concepts, or enriched my imagination. The earlier ones, in particular, are childhood favourites.
- Blindsight and Echopraxia, by Peter Watts.
- Foundation, Foundation and Empire, and Second Foundation, by Isaac Asimov.
- The Remembrance of Earth's Past (地球往事) trilogy, by Liu Cixin (劉慈欣), translated by Ken Liu and Joel Martinsen.
- The Book of Why, by Judea Pearl.
- The Diary of a Young Girl, by Anne Frank.
- Hard-Boiled Wonderland and the End of the World, by Haruki Murakami.
- Ubik, by Philip K. Dick.
- Do Androids Dream of Electric Sheep?, by Philip K. Dick.
- Life of Pi, by Yann Martel.
- The Song of Ice and Fire series, by George R. R. Martin.
- The Name of the Wind and The Wise Man's Fear, by Patrick Rothfuss.
- The Stranger (L’Étranger), by Albert Camus.
- Nineteen Eighty-Four, by George Orwell.
- To Kill a Mockingbird, by Harper Lee.
- The Book Thief, by Markus Zusak.
- The Alchemist, by Paulo Coelho.
- 三字經 (The Three Character Classic), attributed to 王應麟 and/or 區適子.
- 歡樂三國志 (roughly Comedy of the Three Kingdoms), by 侯文詠 (Hou Wenyong) and 蔡康永 (Kevin Tsai). Audiobook.
- Dude, Where's My Country?, by Michael Moore.
- Angels and Demons and The Da Vinci Code, by Dan Brown.
- Airman, by Eoin Colfer.
- The His Dark Materials series, by Philip Pullman.
- The Lord of the Rings trilogy and The Hobbit, by J. R. R. Tolkien.
- The Chronicles of Narnia series, by C. S. Lewis.
- The Artemis Fowl series, by Eoin Colfer.
- The Circle of Magic quartet, by Tamora Pierce.
- Charlotte's Web, by E. B. White.
- The Harry Potter series, by J. K. Rowling.