1. Department of Mathematical Analysis and Numerical Mathematics, Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, 842 48 Bratislava, Slovakia
2. Mathematical Institute of Slovak Academy of Sciences, 814 73 Bratislava, Slovakia
3. STAR-UBB Institute, Bebes-Bolyai University, 400084 Cluj-Napoca, Romania
4. Romanian Institute of Science and Technology, 400487 Cluj-Napoca, Romania
5. Department of Electrical Engineering, City University of Hong Kong, Hong Kong SAR, China