We present some observations on the block triangular form (btf) of structurally symmetric, square, sparse matrices. If the matrix is structurally rank deficient, its canonical btf has at least one underdetermined and one overdetermined block. We prove that these blocks are transposes of each other. We further prove that the square block of the canonical btf, if present, has a special fine struc...

The PT-symmetric square well problem is considered in a SUSY framework when the coupling strength lies below the critical value where PT symmetry becomes spontaneously broken. We find SUSY partner potentials to exist admitting a hierarchy with energy levels depicting an unbroken SUSY situation. Such a hierarchy is a PT-symmetric analogue of the family of sec2-like potentials, to which it reduce...