Alexander C. Li

I'm a first year PhD student in the Machine Learning Department at Carnegie Mellon University. I'm advised by Deepak Pathak, and my work is supported by the National Science Foundation Graduate Research Fellowship.

Previously, I was an electrical engineering and computer science major at UC Berkeley, where I received my BS and MS. I was a researcher in the Berkeley Artificial Intelligence Research Lab and was advised by Pieter Abbeel, Lerrel Pinto, and Carlos Florensa.

In high school, I also spent time at the Hansen Experimental Physics Laboratory, working with Yang Liu on computer vision algorithms for solar physics.

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Research

I'm interested in developing robust, multi-task algorithms for reinforcement learning and unsupervised learning.

Generalized Hindsight for Reinforcement Learning
Alexander C. Li, Lerrel Pinto, Pieter Abbeel
Preprint
arxiv / project page / bibtex

We present Generalized Hindsight: an approximate inverse reinforcement learning technique for relabeling behaviors with the right tasks. Given a behavior generated under one task, Generalized Hindsight finds a different task that the behavior is better suited for. Relabeling a trajectory with this different task and training with an off-policy RL algorithm improves sample-efficiency and asymptotic performance on a suite of multi-task navigation and manipulation tasks.

Sub-policy Adaptation for Hierarchical Reinforcement Learning
Alexander C. Li*, Carlos Florensa*, Ignasi Clavera, Pieter Abbeel
International Conference on Learning Representations (ICLR), 2020
arxiv / project page / bibtex

We develop a new hierarchical RL algorithm that can efficiently adapt pre-trained skills on related tasks, and directly learn effective emergent skills by simultaneously training the entire hierarchy.

Autoregressive Models: What Are They Good For?
Murtaza Dalal*, Alexander C. Li*, Rohan Taori*
Workshop on Information Theory and Machine Learning, NeurIPS, 2019
arxiv / bibtex

We attempt to use powerful autoregressive models for image-to-image translation and outlier detection, with poor results. We analyze the failure modes and find that (a) differentiating through these models creates an ill-conditioned optimization problem and (b) their density estimates are incredibly sensitive to distributional shifts.

Sunspot Rotation and the M-Class Flare in Solar Active Region NOAA 11158
Alexander C. Li & Yang Liu
Solar Physics, 2015
paper / bibtex

We develop a novel algorithm for estimating sunspot rotation speed that is more robust to feature evolution than traditional methods based on time-slices. We use this technique to gain more accurate estimates of magnetic energy buildup in rotating sunspots.

Service
berkeley Head TA, CS 294-158: Deep Unsupervised Learning, Spring 2020

Head Content TA, EECS 126: Stochastic Processes, Fall 2019

TA, CS 188: Artificial Intelligence, Spring 2019

TA, CS 188: Artificial Intelligence, Fall 2018

Academic Intern, CS 189: Machine Learning, Spring 2018

Reader, CS 70: Discrete Mathematics & Probability, Fall 2017
Mentor, Google Code Corps 2017
Awards and Honors

Website template from Jon Barron.