How does a package like ATLAS know which compilers I have installed on my system?For example, say that I install a local version of gfortran, how do I register it in the system so that a package like ATLAS knows that I have it?
How does a package like ATLAS know which fortran compiler to use?
compiling;gcc
Like many unix applications, atlas has a configure script that you run as first part of the build process. Atlas' configure script will try to find a fortran compiler by trying known variants. You can also give it a specific path (-Ss f77lib /path/goes/here) or disable the use of fortran altogether (--nof77)