Best uniform approximation by solutions of elliptic differential equations
P. M. Gauthier, D. Zwick · Transactions of the American Mathematical Society · 1994
We investigate best uniform approximations to continuous functions on compact subsets of R n {\mathbb {R}^n} by solutions of elliptic differential equations and, in particular, by harmonic functions. An axiomatic setting general enough to encompass problems of this kind is given, and in this context we extend necessary and sufficient conditions for best harmonic approximation on precompact Jordan domains to arbitrary compact sets and to more general classes of solutions of linear elliptic differential equations.