An alternative approach to unitoidness
The author extends the work of \textit{C. R. Johnson} and \textit{S. Furtado} [Linear Algebra Appl. 338, 287--290 (2001; Zbl 0993.15011)], who gave a generalization of Sylvester's law of inertia for matrices congruent to a diagonal matrix. Among other things, he expresses the canonical angles of a unitoid matrix \(A\), and their multiplicities, in terms of the eigenvalues and eigenvectors of \(A^{\dagger}A^*\), where \(A^{\dagger}\) is the Moore-Penrose inverse of \(A\).
scientific article; zbMATH DE number 5012989