1. Department of Applied Analysis and Computational Mathematics, Eötvös Loránd University, Pázmány P. stny. 1/C, H-1117 Budapest, Hungary
2. Department of Energy Engineering, Budapest University of Technology and Economics, Bertalan L. u. 4-6, H-1111 Budapest, Hungary
3. Department of Analysis, Budapest University of Technology and Economics, Egry J. u. 1, H-1111 Budapest, Hungary