  We present a method to compute the magnetic moment of a bulk, finite-size,
three-dimensional, anisotropic superconductor. Our numerically implemented
perturbative procedure is based on a solution of the nonlinear Maxwell- London
equations, where we include the nonlinear relation between current and gauge
invariant velocity. The method exploits the small ratio of penetration depth to
sample size. We show how to treat the open boundary conditions over an infinite
domain and the continuity requirement at the interface. We demonstrate how our
method substantially reduces the computational work required and discuss its
implementation to an oblate spheroid. The numerical solution is obtained from a
finite difference method. We briefly discuss the relevance of this work to
similar problems in other fields.
