Institute of Computational Mathematics & Information Technology, Kazan Federal University, Kazan, Russia
Department of Mathematical Sciences, University of Oulu, Oulu, Finland
Tianjin University of Finance and Economics, Tianjin, China
Copyright © 2018 A. Lapin, E. Laitinen et al. This is
an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited.