Kurbatov, Vladimir Georgievich, and Irina Vladimirovna Kurbatova. 2012. “Krylov Subspace Methods of Approximate Solving Differential Equations from the Point of View of Functional Calculus”. Eurasian Mathematical Journal 3 (4):53-80. https://emj.enu.kz/index.php/main/article/view/807.