Test Function Spaces for Geometric Finite Elements

Abstract: We construct test function spaces for geometric finite elements. Geometric finite elements (GFE) are generalizations of Lagrangian finite elements to situations where the unknown function maps into a nonlinear space. Test functions for such spaces arise as variations of GFE functions wherever the GFE function space has a local manifold structure. For any given GFE function $u_h$, the test functions form a linear space that depends on $u_h$. They generalize Jacobi fields in the same way that the GFE interpolation functions generalize geodesic curves. Having test function spaces allows to extend the GFE method to boundary value problems that do not have a minimization formulation.