“…The localization of several roots closest to the origin using the argument principle followed by several Newton iterations can be faster than the localization of all the roots by some general-purpose method. Moreover for more general boundary conditions, e.g., involving multiplication by an analytic function of λ, the approximate characteristic function may not be a polynomial, and the argument principle becomes even more useful (see, e.g., [6,14,53]). The argument principle consists in the following, see, e.g., [10].…”