Heriot-Watt Mathematics Report Series
HWM06-44, 29 Nov 2006

Variational and non-variational eigenvalues of the $p$-Laplacian

B P Rynne and P A Binding


Abstract

It is well known that all the eigenvalues of the linear eigenvalue problem \[ \Delta u = (q - \lambda r) u , \quad \text{ in } \Omega\subset R^N, \] can (under appropriate conditions on $q$, $r$ and $\Omega$) be characterized by minimax principles, but it has been a long-standing question whether that remains true for analogous equations involving the $p$-Laplacian $\Delta_p$. It will be shown that there are corresponding nonlinear eigenvalue problems $$ \Delta_p u = (q - \lambda r) |u|^{p-1}\sgn u, \quad \text{ in } \Omega\subset R^N, $$ with $1 < p \ne 2$ and $q,\, r \in C^1(\overline\Omega)$, for which not all eigenvalues are of variational type. As far as we know, this is the first observation of such a phenomenon, and examples will be given for one and higher dimensional equations. The question of exactly which eigenvalues are variational is also discussed when $N=1$.

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