1. Department of MathematicsLe Quy Don Technical University 236 Hoang Quoc Viet Hanoi Vietnam
2. Faculty of Automatic Control, Electronics and Computer ScienceSilesian University of Technology Akademicka 16, 44‐100 Gliwice Poland
3. Faculty of Mathematics, Center for DynamicsTechnische Universität Dresden Zellescher Weg 12‐14 Dresden 01069 Germany