Optimal Order Finite Element Method for a Coupled Eigenvalue Problem on Overlapping Domains

The aim of this paper is to present a new finite element approach applied to a nonstandard second order elliptic eigenvalue problem, defined on two overlapping domains. We derive optimal error estimates as distinguished from [1], where they are suboptimal. For this purpose we introduce a suitable modified degrees of freedom and a corresponding interpolation operator. In order to fix the ideas and to avoid technical difficulties, we consider an one-dimensional case. The conclusive part presents numerical results.