  We extend the recently proposed semi-Lagrangian algorithm for the extremely
anisotropic heat transport equation [Chac\'on et al., J. Comput. Phys., 272
(2014)] to deal with arbitrary magnetic field topologies. The original scheme
(which showed remarkable numerical properties) was valid for the so-called
tokamak-ordering regime, in which the magnetic field magnitude was not allowed
to vary much along field lines. The proposed extension maintains the attractive
features of the original scheme (including the analytical Green's function,
which is critical for tractability) with minor modifications, while allowing
for completely general magnetic fields. The accuracy and generality of the
approach are demonstrated by numerical experiment with an analytical
manufactured solution.
