1. Department of Environmental Science, Aarhus University, Roskilde, Denmark
2. Institute of Information and Communication Technologies, Bulgarian Academy of Sciences, Sofia, Bulgaria
3. MTA-ELTE Numerical Analysis and Large Networks Research Group, Budapest, Hungary and Institute of Mathematics, Budapest University of Technology and Economics, Egry J. u. 1., 1111, Budapest, Hungary
4. MTA-ELTE Numerical Analysis and Large Networks Research Group, Budapest, Hungary and Department of Applied Analysis and Computational Mathematics, Eötvös Loránd University, Budapest, Hungary