Recently, an extension of this method was presented looking at the ground and 1st excited state energies and wave functions for systems of one (or two) electrons in a 2D (and 3D) potential well having a shape intermediate between a circle and a square (or a sphere and a cube for the case of 3 dimensions). A variety of literature exists exploring these generalized eigenvalue problems, and showcase a range of strategies both analytic and numeric in nature .