文摘
Given a finite set σ of the unit disc and a holomorphic function f in which belongs to a class X, we are looking for a function g in another class Y (smaller than X) which minimizes the norm gY among all functions g such that gσ=fσ. For Y=H∞, and for the corresponding interpolation constant c(σ,X,H∞), we show that where n=#σ, r=maxλσλ and where φX(t) stands for the norm of the evaluation functional ff(λ) on the space X. The upper bound is sharp over sets σ with given n and r. To cite this article: R. Zarouf, C. R. Acad. Sci. Paris, Ser. I 347 (2009).