Ian Putnam: Research

"If we knew what it was we were doing,
it would not be called research, would it?"
- Albert Einstein.


Description of research interests

My research concerns dynamical systems and operator algebras and the close connections between these fields. In particular, I am interested in topological dynamical systems, particularly minimal systems on the Cantor set, systems arising from aperiodic tilings, symbolic dynamical systems and the hyperbolic systems associated with Smale's program for Axiom A dynamics. In operator algebras, I am mainly interested in C*-algebras, groupoid C*-algebras, K-theory for C*-algebras and other aspects of Alain Connes' program in noncommutative geometry.

From a topological dynamical system, there are several constructions of C*-algebras. This provides a fascinating link between the two subjects. On the one hand, it produces interesting examples of C*-algebras. Some, such as the Cuntz-Krieger algebras constructed from subshifts of finite type and the C*-algebras associated with irrational rotations of the circle, have had a fundamental impact on the subject. It is insightful to see how dynamical properties manifest themselves in the C*-algebras. On the other hand, techniques which are used in the study of C*-algebras can often give new information about the dynamics. As a specific example, starting from a dynamical system, constructing the C*-algebra and then taking its K-theory provides an interesting invariant, rather like homology of spaces. In my work on minimal dynamical systems on Cantor sets, I (and my co-workers) used K-theory to obtain a complete invariant for orbit equivalence for many systems. In addition, our work brought many C*-algebra ideas (such as Bratteli diagrams) to effective use in dynamics.

List of Publications

(Indicated papers may be obtained as PDF and/or post-script files)

Unpublished items

Presentations at conferences and workshops