1. Faculty of Physics-Mathematics, Andizhan State University, Andizhan 170100, Uzbekistan
2. School of Engineering, Central Asian University, Tashkent 111221, Uzbekistan
3. V.I. Romanovskiy Institute of Mathematics, Uzbek Academy of Sciences, Tashkent 100174, Uzbekistan
4. Department of Applied Mathematics, Tashkent State University of Economics, Tashkent 100006, Uzbekistan
5. Department of Economics and Political Sciences, University of Aosta Valley, 11100 Aosta, Italy