Professor Stefan Kiefer
Biography
I have been the Tutorial Fellow in Computer Science at St John's College since 2017. I tutor first- and second-year core Computer Science subjects. Previously I had been at St John's as a college lecturer for three years. I have been an Associate Professor in the Department of Computer Science since 2014. In 2009 I completed my PhD at the Technical University of Munich, just before I moved to Oxford.
Teaching
My main teaching activities are giving computer science tutorials to first- and second-year undergraduate students and supervising project and DPhil students. Tutorial teaching is all about communication and understanding each other, so I always try to figure out how students think. I hope this approach is good pedagogy – in any case it’s a hugely rewarding aspect of being a tutor.
Research Interests
My research is motivated by computer-aided verification. The ambition is to analyse computer systems to make sure they behave correctly, which is particularly important for safety-critical systems such as airplanes or medical devices. A wide variety of methods from computer science and mathematics can help with this enormous task: my work involves logics, automata and complexity theory, numerical analysis and linear algebra. I’m particularly interested in the analysis of probabilistic systems, which involve an element of chance, either by design or inevitably. This leads me to study and apply further fields such as probability and queueing theory.
What inspired me?
I liked the idea of instructing a machine to quickly calculate complex things, which would be too cumbersome to compute by hand. This led me to programming. After I graduated from school I chose to study computer science because I hoped I would not have to memorise very much and my being good at Maths would help. I was not disappointed. For me, computer science is all about solving problems. My work as a teacher and researcher allows me to go a step further: when things go well, I solve computer science problems, that is, I solve problems about solving problems!
Selected publications
Dmitry Chistikov, Stefan Kiefer, Ines Marusic, Mahsa Shirmohammadi, and James Worrell. Nonnegative matrix factorization requires irrationality. SIAM Journal on Applied Algebra and Geometry (SIAGA), 1(1):285–307, 2017.
https://doi.org/10.1137/16M1078835
Tomás Brázdil, Stefan Kiefer, Antonín Kučera, and Ivana Hutarová Vareková. Runtime analysis of probabilistic programs with unbounded recursion. Journal of Computer and System Sciences, 81(1):288–310, February 2015.
http://dx.doi.org/10.1016/j.jcss.2014.06.005
Tomás Brázdil, Stefan Kiefer, and Antonín Kučera. Efficient analysis of probabilistic programs with an unbounded counter. Journal of the ACM, 61(6):41:1–41:35, December 2014.
http://dx.doi.org/10.1145/2629599
Javier Esparza, Stefan Kiefer, and Michael Luttenberger. Newtonian program analysis. Journal of the ACM, 57(6):33:1–33:47, October 2010.