Matrix transformation of univalent power series
Frederick W. Hartmann, Thomas H. MacGregor · Journal of the Australian Mathematical Society · 1974
Suppose that A = [αnk], (n, k = 0, 1, 2, …), is an indinite matrix with complex entries. A transforms a complex sequence a = {an to a complex sequence {bn = b = Aa where assuming that the series in (1) converges. Each sequence a = {an is uniquely associated with a power series In this way the matrix A transforms a power series into a power series. Specifically, the power series (2) is mapped to the power series where the bn's are given by (1). We are only interested in matrices having the property that each power series analytic in Δ = {z: |z| < 1} maps to a power series analytic in Δ.