[1] Brno University of Technology, Faculty of Electrical Engineering and Communication, Department of Mathematics, Brno, Czech Republic
[2] Brno University of Technology, Faculty of Civil Engineering, Department of Mathematics and Descriptive Geometry, Brno, Czech Republic
[3] Departamento de Ciências Exatas e Engenharia, Academia Militar, Amadora, Portugal and Peoples' Friendship University of Russia (RUDN), Russia