
ResearchMy research area is scientific computing with main focus on systems and control theory. I am part of the research group Matrix Computations with Applications and the UMIT Research Lab. My main interests are methods and tools for computing nearby Jordan and Kronecker structures and numerical methods for dynamical systems with perodic coefficients. The last is a joint project with the Robotics and Control Lab at Department of Applied Physics and Electronics, Umeå University. PublicationsB. Kågström, S. Johansson, and P. Johansson. StratiGraph Tool: Matrix Stratifications in Control Applications. In L. Biegler, S. L. Campbell, and V. Mehrmann (Eds.): Control and Optimization with DifferentialAlgebraic Constraints, pp 79103, 2012, SIAM Publications. ISBN 9781611972245. Also as Report UMINF11.12. S. Gusev, S. Johansson, B. Kågström, A. Shiriaev, and A. Varga. A Numerical Evaluation of Solvers for the Periodic Riccati Differential Equation. BIT Numerical Mathematics, Vol. 50, pp. 301329, 2010. Also as Report UMINF09.03 (revised). E. Elmroth, S. Johansson, and B. Kågström. Stratification of Controllability and Observability Pairs  Theory and Use in Applications. SIAM J. Matrix Analysis and Applications, Vol. 31, No. 2, pp. 203226, 2009. Also as Report UMINF08.03. S. Gusev, S. Johansson, B. Kågström, A. Shiriaev, and A. Varga. A Numerical Evaluation of Solvers for the Periodic Riccati Differential Equation. Technical report, Umeå University, Department of Computing Science, 2009, UMINF09.03. S. Johansson. Reviewing the Closure Hierarchy of Orbits and Bundles of System Pencils and Their Canonical Forms. Technical report, Umeå University, Department of Computing Science, 2009, UMINF09.02. S. Johansson, B. Kågström, A. Shiriaev, and A. Varga. Comparing oneshot and multishot methods for solving periodic Riccati differential equations. In Proc. of the 3rd IFAC Workshop Periodic Control Systems, PSYCO'07, St Petersburg, Russia, 2007. S. Johansson. Stratification of Matrix Pencils in Systems and Control: Theory and Algorithms. Licentiate Thesis, Umeå University, Department of Computing Science, May, 2005, UMINF05.17, ISBN9173059013. S. Johansson. Canonical forms and stratification of orbits and bundles of system pencils. Technical report, Umeå University, Department of Computing Science, 2005, UMINF05.16. E. Elmroth, P. Johansson, S. Johansson, and B. Kågström. Orbit and Bundle Stratification for Controllability and Observability Matrix Pairs in StratiGraph. In Proc. Sixteenth International Symposium on: Mathematical Theory of Networks and Systems (MTNS), 2004. S. Johansson. Stratification of matrix pairs with applications in control theory (in Swedish). Master's thesis, Umeå University, Department of Computing Science, 2001, UMNAD 373/01. 
Stefan Johansson