pub fn eigen_with_pullback(
a: MatrixView<'_>,
options: EigenOptions,
gap_tolerance: f64,
) -> Result<(SymmetricEigen, EigenPullback), SolverError>pub fn eigen_with_pullback(
a: MatrixView<'_>,
options: EigenOptions,
gap_tolerance: f64,
) -> Result<(SymmetricEigen, EigenPullback), SolverError>