Galba, E. F., V. S. Deineka, and I. V. Sergienko. 2011. “Existence and Uniqueness of Weighted Pseudoinverse Matrices and Weighted Normal Pseudosolutions With Singular Weights”. Ukrains’kyi Matematychnyi Zhurnal 63 (1): 80-101. https://umj.imath.kiev.ua/index.php/umj/article/view/2700.