title: What is the -O5 flag for compiling gfortran .f90 files?
body: <p>I see the flag in the documentation of how to compile some f90 code I have acquired (specifically, mpfi90 -O5 file.f90), but researching the -O5 flag turned up nothing in the gfortran docs, mpfi docs, or anywhere else. I assume it is an optimization flag like -O1, etc., but I'm not sure. </p>
  
  <p>Thanks!</p>