А.N. Kudinov - Dr.Sc. (Phys.-Math.), Professor, Tver State University. E-mail: mathlab@yandex.ru V.N. Ryzikov - Ph.D. (Phys.-Math.), Associated Professor, Tver State University. E-mail: vlr@yandex.ru V.P. Tsvetkov- Dr.Sc. (Phys.-Math.), Professor, Tver State University. E-mail: tsvet@tversu.ru I.V. Tsvetkov- Dr.Sc. (Eng.), Professor, Tver State University. E-mail: tsvet@tversu.ru