[1] Hungarian Acad Sci, Inst Tech Phys & Mat Sci, Res Ctr Nat Sci, H-1525 Budapest, Hungary
[2] Univ Leeds, Sch Math, Dept Appl Math, Leeds LS2 9JT, W Yorkshire, England
[3] Wenzhou Univ, Coll Phys & Elect Informat Engn, Wenzhou 325035, Peoples R China
[4] Univ Maribor, Fac Nat Sci & Math, SLO-2000 Maribor, Slovenia