PR #47 uses the Vandermonde matrix to build eigenvectors analytically when analytic poles are available. The same approach should work in the polynomial ZOH path: call consteig::eigenvalues() on the companion matrix (which we have shown to be reasonably accurate), then construct the Vandermonde matrix from those eigenvalues instead of calling consteig::eigenvectors(). This would extend the eigenvector accuracy improvement to AnalogFilter users who only have polynomial coefficients.
PR #47 uses the Vandermonde matrix to build eigenvectors analytically when analytic poles are available. The same approach should work in the polynomial ZOH path: call consteig::eigenvalues() on the companion matrix (which we have shown to be reasonably accurate), then construct the Vandermonde matrix from those eigenvalues instead of calling consteig::eigenvectors(). This would extend the eigenvector accuracy improvement to AnalogFilter users who only have polynomial coefficients.