Norms of composition operators with rational symbol (Q852824)

Among the analytic selfmaps \(\phi\) on the unit disc which are non-inner rational functions in \({\mathbb C^*}\), the authors find a collection where the norm of the composition operator \(\| C_\phi\| \) on the Hardy space \(H^2\) can be computed from a given quadratic expression. They compare their results with those proved by \textit{C. Hammond} [Acta Sci. Math. 69, No. 3--4, 813--829 (2003; Zbl 1071.47508)] in the case of linear fractional maps and the one by \textit{C. C. Cowen} [Integral Equations Oper. Theory 11, No. 2, 151--160 (1988; Zbl 0638.47027)] for linear maps.