A well–known property of an irreducible singular M–matrix is that it has a generalized inverse which is non–negative, but this is not always true for any generalized inverse. The authors have characterized when the Moore–Penrose inverse of a symmetric, singular, irreducible and tridiagonal M–matrix is itself an M–matrix. We aim here at giving new explicit examples of infinite families of matric...

Four results are given that address the existence, ambiguities and construction of a classical R-matrix given a Lax pair. They enable the uniform construction of R-matrices in terms of any generalized inverse of ad(L). For generic L a generalized inverse (and indeed the Moore-Penrose inverse) is explicitly constructed. The R-matrices are in general momentum dependent and dynamical. We apply our...

Closed-form formulas are derived for the rank and inertia of submatrices of the Moore–Penrose inverse of a Hermitian matrix. A variety of consequences on the nonsingularity, nullity and definiteness of the submatrices are also presented.