Matrix representation of the resolvent operator in square-integrable basis and physical application

We obtain simple formulas for the matrix elements of the resolvent operator (the Green’s function) in any finite set of square integrable basis. These formulas are suitable for numerical computations whether the basis elements are orthogonal or not. A byproduct of our findings is an expression for the normalized eigenvectors of a matrix in terms of its eigenvalues. We give a physical application as an illustration of how useful these results can be.