The compilation compound for PLATON should look like: (sudo) gfortran -o platon platon.f xdrvr.c -L/usr/X11R6/lib -lX11 sudo appears to be needed for compilation on Mac OS X/Yosemite but not with linux distributions. Mac OS X Yosemite: Install the latest XQuartz, gfortran, gcc, Xcode and command line tools