Tuesday, 16 May 2017

real analysis - Uniform convergence of derivatives

The following is taken from Rudin's Principles of Mathematical Analysis; it is Theorem 7.17 with some extra assumptions made based on a remark at the end of the proof of the theorem.



Let fn,g be functions defined on an interval [a,b]. Assume that fn are differentiable with continuous derivatives. Assume also that fng uniformly and fnf pointwise in [a,b] for some function f (or more generally, assume that fn(xo) is convergent for some xo[a,b]). Then, fnf uniformly, f is differentiable with continuous derivative and f=g.




Does a similar result hold for holomorphic functions on an open set? Since Rudin speaks of intervals, should such a result be valid for connected or convex sets only, instead of open sets in general? Namely, if Ω is a domain and fn are holomorphic functions on Ω, does uniform convergence of fn on the whole domain (not uniform convergence on compacts subsets of the domain!) plus pointwise convergence of fn, imply uniform convergence of fn on the whole domain?

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