Harnack's principle

Harnack's principle   (Redirected from Harnack's theorem) Jump to navigation Jump to search In complex analysis, Harnack's principle or Harnack's theorem is one of several closely related theorems about the convergence of sequences of harmonic functions, that follow from Harnack's inequality.

If the functions {displaystyle u_{1}(z)} , {displaystyle u_{2}(z)} , ... are harmonic in an open connected subset {displaystyle G} of the complex plane C, and {displaystyle u_{1}(z)leq u_{2}(z)leq dots } in every point of {displaystyle G} , then the limit {displaystyle lim _{nto infty }u_{n}(z)} either is infinite in every point of the domain {displaystyle G} or it is finite in every point of the domain, in both cases uniformly in each compact subset of {displaystyle G} . In case the limits are finite, the limit function {displaystyle u(z)=lim _{nto infty }u_{n}(z)} is harmonic in {displaystyle G} .

References Kamynin, L.I. (2001) [1994], "Harnack theorem", Encyclopedia of Mathematics, EMS Press This article incorporates material from Harnack's principle on PlanetMath, which is licensed under the Creative Commons Attribution/Share-Alike License. Categories: Harmonic functionsTheorems in complex analysisMathematical principles