Weyl discs in the degenerate Schur interpolation problem (Q1190042)

The author enlarges upon some results given in a series of papers by \textit{V. K. Dubovoj} [Teor. Funkts. Anal. Prilozh 37, 14-26 (1982; Zbl 0541.41002), ibid. 38, 32-39 (1982; Zbl 0573.41012), ibid. 41, 55-64 (1984; Zbl 0601.30044), ibid. 42, 46-57 (1984; Zbl 0601.41003)]. The set of solutions to the Schur problem with data matrix \(C_ n\) at a fixed point \(\zeta_ 0\), \(0<|\zeta_ 0|<1\), forms a matrix disk, the Weyl disk, and this paper is concerned with representations of the radii of these disks. Several such representations are given for both left and right radii, and the limits of these radii are considered for a sequence \(\{C_ n\}\) of data matrices. Statements of the results are quite technical.