Institute for Systems Theory and Automatic Control, Pfaffenwaldring 9, 70550 Stuttgart, Germany. andrei.kramer@ist.uni-stuttgart.de.|Institute for Systems Theory and Automatic Control, Pfaffenwaldring 9, 70550 Stuttgart, Germany. andrei.kramer@ist.uni-stuttgart.de.|Institute for Systems Theory and Automatic Control, Pfaffenwaldring 9, 70550 Stuttgart, Germany. andrei.kramer@ist.uni-stuttgart.de.