Convergent Interpolation to Cauchy Integrals of Jacobi-type Weights and RH∂-Problems

Analysis Seminar
Wednesday, September 23, 2009 - 2:00pm for 1 hour (actually 50 minutes)
Skiles 269
Maxym Yattselev – Vanderbilt University
Brett Wick
We consider multipoint Padé approximation to Cauchy transforms of complex measures. First, we recap that if the support of a measure is an analytic Jordan arc and if the measure itself is absolutely continuous with respect to the equilibrium distribution of that arc with Dini-continuous non-vanishing density, then the diagonal multipoint Padé approximants associated with appropriate interpolation schemes converge locally uniformly to the approximated Cauchy transform in the complement of the arc. Second, we show that this convergence holds also for measures whose Radon–Nikodym derivative is a Jacobi weight modified by a Hölder continuous function. The asymptotics behavior of Padé approximants is deduced from the analysis of underlying non–Hermitian orthogonal polynomials, for which the Riemann–Hilbert–∂ method is used.