Inverse problems for semilinear elliptic PDE with a general nonlinearity $a(x,u)$

Abstract

This article studies the inverse problem of recovering a nonlinearity in an elliptic equation $\hat{I}”u+a(x,u)=0$ from boundary measurements of solutions. Previous results based on first order linearization achieve this under a sign condition on ${\partial }_{u}a(x,u)$, and results based on higher order linearization recover the Taylor series of $a(x,u)$ with respect to $u$. We improve these results and show that a general nonlinearity, and not just its Taylor series, is uniquely determined up to gauge near a fixed solution. Our method is based on constructing a good solution map that locally parametrizes solutions of the nonlinear equation by solutions of the linearized equation.

Final draft