1. Department of Mathematics and Mechanics, Novosibirsk State University, Pirogova Str. 2, Novosibirsk 630090, Russia
2. Lavrentyev Institute of Hydrodynamics SB RAS, Lavrentyev Pr. 15, Novosibirsk 630090, Russia
3. Basic Studies Department, Siberian State University of Telecommunications and Information Science, Kirova Str. 86, Novosibirsk 630102, Russia