1. Mathematical Analysis Department, Chelyabinsk State University, Kashirin Brothers Str., 129, Chelyabinsk, 454001; and South Ural State Universiry (National Research University), Lenin Av., 76, Chelyabinsk, Russia, 454080
2. Computational Mechanics Department, South Ural State University (National Research University), Lenin Avenue, 76, Chelyabinsk, Russia, 454080