## Research

I work in an area of mathematics called *noncommutative algebra*, specifically in *noncommutative algebraic geometry*, and *noncommutative invariant theory*. I also enjoy thinking about certain problems in combinatorics (in particular, about capsets in **F**_{3}^{n}).

#####
In noncommutative algebra, we study mathematical structures (called rings) whose multiplication operation is not necessarily commutative. Such mathematical structures are actually ubiquitous.

If you have taken linear algebra, then you have seen that the set of all 2x2 matrices with entries in **R** has a natural multiplication, but for two matrices *A* and *B*, the products *AB* and *BA* are different, in general. One way to understand this phenomenon is that *A* and *B* can be viewed as linear transformations **R**^{2} → **R**^{2}, where multiplication of matrices corresponds to composition of functions. And, of course, the order in which you compose functions matters (your day turns out very differently if you first put on your shoes and then your socks vs. first putting on your socks and then your shoes).

Noncommutative rings also arise naturally in quantum mechanics (the position and momentum operators do not commute), conformal field theory (where symmetries are captured by so-called quantum groups), the study of Lie algebras (the universal enveloping algebra a Lie algebra is not necessarily commutative), and the study of differential operators (multiplication by *t* and differentiation *d/dt* do not commute).

I study noncommutative rings using both ring-theoretic and homological techniques. I also study Hopf algebras and weak Hopf algebras, and their actions on rings. If you'd like to learn more about noncommutative algebra, I can recommend the following:

- An Invitation to Noncommutative Algebra by Chelsea Walton
- Invariant Theory of Artin-Schelter Regular Algebras: A survey by Ellen Kirkman
- An Introduction to Noncommutative Projective Geometry by Daniel Rogalski.

**R**has a natural multiplication, but for two matrices

*A*and

*B*, the products

*AB*and

*BA*are different, in general. One way to understand this phenomenon is that

*A*and

*B*can be viewed as linear transformations

**R**

^{2}→

**R**

^{2}, where multiplication of matrices corresponds to composition of functions. And, of course, the order in which you compose functions matters (your day turns out very differently if you first put on your shoes and then your socks vs. first putting on your socks and then your shoes).

*t*and differentiation

*d/dt*do not commute).

#####
Consider *n*-dimensional affine space **F**_{3}^{n} over the field with three elements.
A *capset* in **F**_{3}^{n} is a collection of points in which no three points are collinear.
Finding the largest possible capset in **F**_{3}^{n} is a very difficult problem (in fact, the exact answer is not known when *n* > 6). One interesting and useful fact is: although the definition of a capset is geometric, there is an equivalent arithmetic definition. A subset of **F**_{3}^{n} is a capset if and only if it contains no three-term arithmetic progressions. Hence, techniques of combinatorial number theory can (and have) been used to study capsets

I learned about capsets as an undergraduate at Lafayette College's REU. Since then, I have advised several student projects of my own related to capsets. It turns out that the affine geometric space **F**_{3}^{4} can be visualized using the deck of cards from the game SET. My REU mentor Liz McMahon (together with her family) wrote a great book on the mathematics of SET.

*The Joy of SET* by Liz McMahon, Gary Gordon, Hannah Gordon, and Rebecca Gordon.

*n*-dimensional affine space

**F**

_{3}

^{n}over the field with three elements. A

*capset*in

**F**

_{3}

^{n}is a collection of points in which no three points are collinear. Finding the largest possible capset in

**F**

_{3}

^{n}is a very difficult problem (in fact, the exact answer is not known when

*n*> 6). One interesting and useful fact is: although the definition of a capset is geometric, there is an equivalent arithmetic definition. A subset of

**F**

_{3}

^{n}is a capset if and only if it contains no three-term arithmetic progressions. Hence, techniques of combinatorial number theory can (and have) been used to study capsets

**F**

_{3}

^{4}can be visualized using the deck of cards from the game SET. My REU mentor Liz McMahon (together with her family) wrote a great book on the mathematics of SET.

*The Joy of SET*by Liz McMahon, Gary Gordon, Hannah Gordon, and Rebecca Gordon. My Erdős number is 3 (via two paths: *Michael Tait→Fan Chung→Paul Erdős* and *Thang Pham→Arie Bialostocki→Paul Erdős*).

In a past life, I did some research in neuroscience. Those papers can be found at the bottom of this page.

### Publications

#####
Fixed rings of generalized Weyl algebras

with Jason Gaddis.

*Journal of Algebra*, Volume 536, 149–169. (2019).
Journal

arXiv
Sidon sets and 2-caps in **F**_{3}^{n}

with Yixuan (Alice) Huang and Michael Tait.

*Involve, a Journal of Mathematics*, Vol. 12, No. 6, 995–1003. (2019).

Alice is a Wake Forest undergraduate who was awarded a Wake Forest Research Fellowship to work with me during the summer of 2018. She presented a poster at Wake Forest's Undergraduate Research Day.
Journal

arXiv

C++ code
Auslander's Theorem for permutation actions on noncommutative algebras

with Jason Gaddis, Ellen Kirkman, and W. Frank Moore.

*Proceedings of the American Mathematical Society* **147**, 1881–1896. (2019).
Journal

arXiv
Discriminants of Taft algebra smash products and applications

with Jason Gaddis and Daniel Yee.

*Algebras and Representation Theory*, Volume 22, Issue 4, 785–799. (2019).
Journal

arXiv
The noncommutative schemes of generalized Weyl algebras.

*Journal of Algebra*, Volume 506, 322–349. (2018).
Journal

arXiv
The Picard group of the graded module category of a generalized Weyl algebra.

*Journal of Algebra*, Volume 493, 89–134. (2018).
Journal

arXiv
A structure theorem for product sets in extra special groups

with Thang Pham, Michael Tait, and Le Anh Vinh.

*Journal of Number Theory*, Volume 184, 461–472. (2018).
Journal

arXiv
Partitions of *AG*(4,3) into maximal caps

with Michael Follett, Kyle Kalail, Elizabeth McMahon, and Catherine Pelland.

*Discrete Mathematics*, Volume 337, 1–8. (2014).
Journal

arXiv
The graded module category of a generalized Weyl algebra.

Ph.D. thesis, University of California, San Diego (2016).
eScholarship

pdf

with Jason Gaddis.

*Journal of Algebra*, Volume 536, 149–169. (2019).arXiv

**F**_{3}^{n}with Yixuan (Alice) Huang and Michael Tait.

*Involve, a Journal of Mathematics*, Vol. 12, No. 6, 995–1003. (2019).Alice is a Wake Forest undergraduate who was awarded a Wake Forest Research Fellowship to work with me during the summer of 2018. She presented a poster at Wake Forest's Undergraduate Research Day.

arXiv

C++ code

with Jason Gaddis, Ellen Kirkman, and W. Frank Moore.

*Proceedings of the American Mathematical Society***147**, 1881–1896. (2019).arXiv

with Jason Gaddis and Daniel Yee.

*Algebras and Representation Theory*, Volume 22, Issue 4, 785–799. (2019).arXiv

*Journal of Algebra*, Volume 506, 322–349. (2018).arXiv

*Journal of Algebra*, Volume 493, 89–134. (2018).arXiv

with Thang Pham, Michael Tait, and Le Anh Vinh.

*Journal of Number Theory*, Volume 184, 461–472. (2018).arXiv

*AG*(4,3) into maximal capswith Michael Follett, Kyle Kalail, Elizabeth McMahon, and Catherine Pelland.

*Discrete Mathematics*, Volume 337, 1–8. (2014).arXiv

Ph.D. thesis, University of California, San Diego (2016).

### Preprints

#####
Semisimple reflection Hopf algebras of dimension sixteen

with Luigi Ferraro, Ellen Kirkman, and W. Frank Moore.
arXiv
Simple **Z**-graded domains of Gelfand-Kirillov dimension two

with Luigi Ferraro and Jason Gaddis.
arXiv
Three infinite families of reflection Hopf algebras

with Luigi Ferraro, Ellen Kirkman, and W. Frank Moore.
arXiv

with Luigi Ferraro, Ellen Kirkman, and W. Frank Moore.

**Z**-graded domains of Gelfand-Kirillov dimension twowith Luigi Ferraro and Jason Gaddis.

with Luigi Ferraro, Ellen Kirkman, and W. Frank Moore.

### Invited Talks

#####
"A proof of the Brown-Goodearl conjecture for module-finite weak Hopf algebras"

AMS Western Sectional Meeting, Riverside, CA, November 2019
"A translation principle for generalized Weyl algebras"

AMS Central Sectional Meeting, Madison, WI, September 2019
Slides
"The card game SET, finite affine geometry, and combinatorial number theory"

Portland State University Colloquium, Portland, OR, May 2019
Slides
"A translation principle for generalized Weyl algebras"

AMS Central/Western Sectional Meeting, Honolulu, HI, March 2019
Slides

Abstract
"**Z**-graded noncommutative algebraic geometry"

University of Washington Algebra/Algebraic Geometry Seminar, Seattle, WA, February 2018
Slides
"Simple **Z**-graded domains of Gelfand-Kirillov dimension 2"

AMS-MAA Joint Mathematics Meetings, San Diego, CA, January 2018
Slides

Abstract
"**Z**-graded noncommutative algebraic geometry"

Miami University Colloquium, Oxford, OH, November 2017
Slides
"Noncommutative invariant theory and Auslander's Theorem"

Miami University Algebra Seminar, Oxford, OH, November 2017
Slides
"Discriminants of Taft algebra smash products and applications"

AMS Central Sectional Meeting, Denton, TX, September 2017
Slides

Abstract
"Auslander's Theorem for permutation actions on noncommutative algebras"

AMS Western Sectional Meeting, Pullman, WA, April 2017
Slides

Abstract
"The noncommutative schemes of generalized Weyl algebras"

AMS Western Sectional Meeting, Denver, CO, October 2016
Slides

Abstract
"The noncommutative schemes of generalized Weyl algebras"

AMS Eastern Sectional Meeting, Brunswick, ME, September 2016
Slides

Abstract
"The category of graded modules of a generalized Weyl algebra"

AMS Central Sectional Meeting, East Lansing, MI, March 2015
Slides

Abstract

AMS Western Sectional Meeting, Riverside, CA, November 2019

AMS Central Sectional Meeting, Madison, WI, September 2019

Portland State University Colloquium, Portland, OR, May 2019

AMS Central/Western Sectional Meeting, Honolulu, HI, March 2019

Abstract

**Z**-graded noncommutative algebraic geometry"University of Washington Algebra/Algebraic Geometry Seminar, Seattle, WA, February 2018

**Z**-graded domains of Gelfand-Kirillov dimension 2"AMS-MAA Joint Mathematics Meetings, San Diego, CA, January 2018

Abstract

**Z**-graded noncommutative algebraic geometry"Miami University Colloquium, Oxford, OH, November 2017

Miami University Algebra Seminar, Oxford, OH, November 2017

AMS Central Sectional Meeting, Denton, TX, September 2017

Abstract

AMS Western Sectional Meeting, Pullman, WA, April 2017

Abstract

AMS Western Sectional Meeting, Denver, CO, October 2016

Abstract

AMS Eastern Sectional Meeting, Brunswick, ME, September 2016

Abstract

AMS Central Sectional Meeting, East Lansing, MI, March 2015

Abstract

### Other Talks

#####
"The geometry of the card game SET"

Loyola Marymount University Math Club, Los Angeles, CA, September 2019
"Algebraic structures in comodule categories over weak Hopf algebras"

Seattle Noncommutative Algebra Day, Seattle, WA, July 2019
"SET and *AG*(4,3)"

Wake Forest Combinatorics Seminar, Winston-Salem, NC, October 2016
Slides
"Categories of graded modules: What they are and what you can do with them"

GradSWANTAG III, La Jolla, CA, May 2016
"The graded module category of a generalized Weyl algebra"

UC San Diego Final Defense, La Jolla, CA, May 2016
Slides

Abstract
"The category of graded modules of a generalized Weyl algebra"

AMS-MAA Joint Mathematics Meetings, Seattle, WA, January 2016
Slides

Abstract
"**Z**-graded noncommutative projective geometry"

UC San Diego Algebra Seminar, La Jolla, CA, November 2015
Slides

Pre-talk

Abstract
"What is noncommutative algebraic geometry?"

UC San Diego Graduate Algebraic Geometry Seminar, La Jolla, CA, August 2015
Slides
"A (gentle) introduction to Hopf algebras"

UC San Diego Informal Noncommutative Algebra Seminar, La Jolla, CA, June 2015
"SET and *AG*(4,3)"

UC San Diego Food For Thought Seminar, La Jolla, CA, February 2015
Slides

Abstract
"Graded modules over generalized Weyl algebras"

UC San Diego Advancement to Candidacy, La Jolla, CA, December 2014
Slides
"SET and disjoint complete caps in *AG*(4,3)"

AMS-MAA Joint Mathematics Meetings, New Orleans, LA, January 2011
Abstract

Loyola Marymount University Math Club, Los Angeles, CA, September 2019

Seattle Noncommutative Algebra Day, Seattle, WA, July 2019

*AG*(4,3)"Wake Forest Combinatorics Seminar, Winston-Salem, NC, October 2016

GradSWANTAG III, La Jolla, CA, May 2016

UC San Diego Final Defense, La Jolla, CA, May 2016

Abstract

AMS-MAA Joint Mathematics Meetings, Seattle, WA, January 2016

Abstract

**Z**-graded noncommutative projective geometry"UC San Diego Algebra Seminar, La Jolla, CA, November 2015

Pre-talk

Abstract

UC San Diego Graduate Algebraic Geometry Seminar, La Jolla, CA, August 2015

UC San Diego Informal Noncommutative Algebra Seminar, La Jolla, CA, June 2015

*AG*(4,3)"UC San Diego Food For Thought Seminar, La Jolla, CA, February 2015

Abstract

UC San Diego Advancement to Candidacy, La Jolla, CA, December 2014

*AG*(4,3)"AMS-MAA Joint Mathematics Meetings, New Orleans, LA, January 2011

### Non-math Publications

#####
Appelbaum, L.G., Boehler, C.N., Davis, L.A., **Won, R.J.**, Woldorff, M.G. (2014). "The dynamics
of proactive and reactive cognitive control processes in the human brain". *Journal of Cognitive
Neuroscience*. 26(5), 1021–1038.
Journal

PubMed
Appelbaum, L.G., Boehler, C.N., **Won, R.J.**, Davis, L.A., Woldorff, M.G. (2012). "Strategic
Allocation of Attention Reduces Temporally Predictable Stimulus Conflict". *Journal of Cognitive Neuroscience*. 24(9), 1834–1848.
Journal

PubMed

**Won, R.J.**, Woldorff, M.G. (2014). "The dynamics of proactive and reactive cognitive control processes in the human brain".*Journal of Cognitive Neuroscience*. 26(5), 1021–1038.PubMed

**Won, R.J.**, Davis, L.A., Woldorff, M.G. (2012). "Strategic Allocation of Attention Reduces Temporally Predictable Stimulus Conflict".*Journal of Cognitive Neuroscience*. 24(9), 1834–1848.PubMed