Asymptotics of Hermite–Padé Rational Approximants for Two Analytic Functions with Separated Pairs of Branch Points (Case of Genus 0)
1 Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, Miusskaya Square 4, 125047 Moscow, Russian Federation
2 Department of Mathematics, Katholieke Universiteit Leuven, Celestijnenlaan 200B box 2400, BE-3001 Leuven, Belgium
Correspondence: Correspondence to be sent to: Walter Van Assche, Department of Mathematics, Katholieke Universiteit Leuven, Celestijnenlaan 200B box 2400, BE-3001 Leuven, Belgium. e-mail: walter{at}wis.kuleuven.be
We investigate the asymptotic behavior for type II Hermite–Padé approximation to two functions, where each function has two branch points and the pairs of branch points are separated. We give a classification of the cases such that the limiting counting measures for the poles of the Hermite–Padé approximants are described by an algebraic function h of order and genus 0. This situation gives rise to a vector-potential equilibrium problem for measures
, µ1, and µ2, and the poles of the common denominator are asymptotically distributed like
/2. We also work out the strong asymptotics for the corresponding Hermite–Padé approximants by using a 3 x 3 Riemann–Hilbert problem that characterizes this Hermite–Padé approximation problem.