S. V. Zhestkov and E. A. . Ermolaev, “One algebraic method to study stability of linear normal systems in partial derivatives”, Ukr. Mat. Zhurn., vol. 44, no. 4, pp. 480–489, Apr. 1992, Accessed: Apr. 09, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/7889