1. Department of Differential Equations; Institute of Mathematics and Mathematical Modeling; 125 Pushkin St 050010 Almaty Kazakhstan
2. Al-Farabi Kazakh National University; 71 Al-Farabi Ave Almaty 050040 Kazakhstan
3. LaSIE, Faculté des Sciences et Technologies; Université de La Rochelle; A. M. Crépeau 17042 La Rochelle France