1. Department of Mathematical Methods and Operations Research,
Faculty of Management Science and Informatics, University of Žilina, Žilina, Slovakia
2. Department of Mathematical Methods and Operations Research, Faculty of Management Science and Informatics, University of Žilina, Žilina, Slovakia
3. Department of Economics and Quantitative Methods, Faculty of Economics,
University of West Bohemia in Pilsen, Univerzitni 22, 306 14 Plzeň, Czech Republic