1. Department of Applied Analysis and Computational Mathematics Eötvös Loránd University Pázmány Péter sétány 1/c. Budapest H‐1117 Hungary
2. Alfréd Rényi Institute of Mathematics Reáltanoda utca 13‐15 Budapest H‐1053 Hungary
3. BBS University of Applied Sciences Alkotmány u. 9 Budapest H‐1054 Hungary