Hi, I appreciate all you links. Perhaps after having some basic knowledge, then such source code could save months, but if you don't even know what to look for, then I would not do that unless I wanted to torture myself. -- The best way to learn how to use some equation is to see someone apply it on some simple case scenario. Teach a man how to fish...This is the closest thing to a simulation of an orbit in GR available on the internet http://www.fourmilab.ch/gravitation/orbits/ for the very limited case of a low mass test particle orbiting a massive body that has a mass that is many orders of magnitude larger than the mass of the test particle. The source of the applet is downloadable for anyone who wants to see the equations used. It does not seem to include orbital decay due to gravitational radiation but that is probably reasonable for a test particle of insignificant mass. I think the program uses exact GR equations which are possible for this very limited case, rather than numerical aproximations, but it might still be of interest.