Daniele Boffi, Zhongjie Lu & Luca F. Pavarino. (2021). Iterative ILU Preconditioners for Linear Systems and Eigenproblems.
            <i>Journal of Computational Mathematics</i>. <i>39</i> (4).
            633-654.
         doi:10.4208/jcm.2009-m2020-0138