In this paper, we prove a
sharp lower bound of the first (nonzero) eigenvalue of the anisotropic Laplacian with
the Neumann boundary condition. Equivalently, we prove an optimal anisotropic
Poincaré inequality for convex domains, which generalizes the classical result
of Payne and Weinberger. A lower bound of the first (nonzero) eigenvalue
of the anisotropic Laplacian with the Dirichlet boundary condition is also
proved.
Keywords
anisotropic Laplacian, first eigenvalue, gradient estimate,
optimal Poincaré inequality