About me

I was born in the Netherlands and did my undergraduate study at the Radboud Universiteit in Nijmegen. I moved to Switzerland and received my PhD in mathematics from the University of Basel in 1997 under supervision of Hanspeter Kraft. I was a postdoc at Northeastern University 1997-1998 and a Moore Instructor at MIT from 1998 until 2000. I was a faculty at the University of Michigan for 20 years until I moved to Northeastern University in 2020.

One of my core research areas is Invariant Theory. I have been particularly interested in upper bounds for the degrees of generators of an invariant ring. Together with Gregor Kemper I wrote a book on Computational Invariant Theory. I have also done a lot of research in the representation theory of quivers and finite dimensional algebras with applications to other areas such as questions about Littlewood-Richardson coefficients and the theory of cluster algebras. Together with Jerzy Weyman I wrote the book An Introduction to Quiver Representations and many research papers. I have also published papers in Combinatorics (e.g. (poly)-matroid invariants), Number Theory (e.g., the Skolem-Mahler-Lech theorem and S-unit equations in positive characteristic) and commutative algebra (e.g. ideals of subspace arrangements). More recently, I have ventured out in areas of applied mathematics. I have worked on Generalized Principal Component Analysis, a method to approximate data with subspace arrangements. I collaborate with the Michigan Center for Integrative Research in Critical Care (MCIRCC) at the University of Michigan to combine tensor decompositions, probabilistic automata and other mathematical techniques with machine learning, signal and image processing and apply these techniques to health care applications such as the detection/prediction of heart arrhythmia, Acute Respiratory Distress Syndrome (ARDS) and sepsis.

In recent years I have been particularly interested in tensors. Tensors are higher-dimensional arrays and are ubiquitous in many data applications. But there are also interesting connections to Algebraic Complexity Theory and Invariant Theory. Some topics I have studied recently relate to various notions of singular values and rank for higher order tensors.

Mathematical problem solving is a passion of mine. I competed in the International Mathematics Olympiad (IMO) in 1988 (bronze medal) and have been involved with mathematics competitions since. I have authored problems for the Dutch Mathematics Olympiad, the IMO (specifically 1989-3, 1990-6 and 1991-3) and was on the questions committee of the William Lowell Putnam Competition from 2016-2018. I have also trained students for the IMO and for the Putnam Competition.

Non-mathematical interests include hiking, playing piano/organ in a rock band and martial arts (Tae Kwon Do).