Affiliation: | a Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovi?a 6, 21000 Novi Sad, Serbia b Department of Mathematics and Informatics, University of Novi Sad, Trg Dositeja Obradovi?a 4, 21000 Novi Sad, Serbia c Óbuda University, Doberdó út 6, H-1034 Budapest, Hungary |