[1] Obuda Univ, Physiol Controls Res Ctr, Budapest, Hungary
[2] Budapest Univ Technol & Econ, Inst Math, Dept Anal & Operat Res, Budapest, Hungary
[3] Univ Maribor, Fac Elect Engn & Comp Sci, Maribor, Slovenia
[4] Univ Maribor, Ctr Appl Math & Theoret Phys, Maribor, Slovenia
[5] Univ Maribor, Fac Nat Sci & Math, Maribor, Slovenia
[6] Budapest Univ Technol & Econ, Inst Math, Dept Anal & Operat Res, Muegyetem Rkp 3, H-1111 Budapest, Hungary