\section{{\tt pde}}
The IDL procedure
\linkf{{\tt pde}}
{http://www.astro.ku.dk/\~{}milvang/RelViz/idl/pde.pro}
was provided by Nordlund/Brandenburg.
It solves 
\hyperref
{the geodesics equation}
{the geodesics equation (equation (}
{)}
{eq:geod}.
