You can define your own SYSTYPE and tell Gadget where you’ve installed GSL and FFTW. By default, they’re in /usr/local/. The MPI library that comes with OS X is in /usr/lib/.Now you’re almost done! Just save the changes you’ve made, exit out of your editor and run “make” in the Gadget-2 code directory. That should produce an executable called Gadget2 that you can run simulations with.There are a number of test cases that come with Gadget. You might try running the galaxy collision test since it makes some nice looking outputs that can be readily visualized using IDL routines included with Gadget. To run the galaxy collision test, first set up a folder with all of the needed executables and parameter files: