CAUTION: Only for
symmetric (Hermitian) eigenproblems may the user assume that a computed Ritz
value is an accurate approximation to an eigenvalue of `OP`.
As § 4.6
of Chapter 4 explained, determining whether an IRAM computes accurate
eigenvalues for non-symmetric (non Hermitian) eigenproblems depends on the
sensitivity of the eigenproblem. If `OP` arises from a
shift-invert spectral transformation,
then the eigenvector purification
step performed by `XYeupd` will most likely result in smaller
residuals for the original problem than those
obtained for `OP` (See (4.5.1) in Chapter 4).