Existence and perturbation of principal eigenvalues for a periodic-parabolic problem
We give a necessary and sufficient condition for the existence of a positive principal eigenvalue for a periodic-parabolic problem with indefinite weight function.The condition was originally established Nail Tools by Beltramo and Hess [extit{frenchspacing Comm.Part.Diff.Eq.}, extbf{9} (1984), 919--941] in the framework of the Schauder theory of cl