1. Existence of harmonic maps
James Eells, Luc Lemaire · Regional conference series in mathematics · 1983
(1.1) A map between Riemannian manifolds is harmonic if the divergence of its differential vanishes. (Those terms will be defined in §3.) Such maps are the extrema ( = critical points) of the energy functional. More precisely, if : M-* • N is a map between Riemannian manifolds, we define