Huang, Zhuo-Hong, and Ting-Zhu Huang. “A Constraint Preconditioner for Solving Symmetric Positive Definite Systems and Application to the Helmholtz Equations and Poisson Equations”. Mathematical Modelling and Analysis 15, no. 3 (July 15, 2010): 299-311. Accessed April 19, 2024. https://journals.vilniustech.lt/index.php/MMA/article/view/6024.