1. Department of Mathematical Sciences, Chalmers University of Technology, and the University of Gothenburg, Gothenburg, Sweden.
2. Signal Processing Laboratory, LTS 4, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
3. School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA 30332 USA.
4. Division of Optimization and Systems Theory, Department of Mathematics, KTH Royal Institute of Technology, Stockholm, Sweden.