title: Running MPI fortran code sample make file
body: <p>I am given a code to run on clusters, and the .sh file content is as below:</p>
  
  <pre><code>compiler  =  mpifort
  
  in8.3     =  mac-ns-2d.8.3.f90
  
  out       =  a.out
  
  inc       =  hypre/include
  
  libs      =  src/hypre/lib
  
  opts      =  -O4
  
  8.3:
      $(compiler) $(opts) -I$(inc) $(in8.3) -o $(out) -L$(libs) -lHYPRE -lm -lstdc++
  </code></pre>
  
  <p>I see what is the first line, which is my compiler mpifortran, but what is the second line meaning, in8.3?
  I also know the meaning for out, inc, libs, but what is the purpose of opts -04 and what does 8.3: mean and the line after that?</p>