title: question on C preprocessor definitions
body: <p>Hi I am currently installing a software called super LU and in the README file there is the following instruction for modifying a makefile depending on system set-up. </p>
  
  <p>C preprocessor definition CDEFS.
     In the header file SRC/Cnames.h, we use macros to determine how
     C routines should be named so that they are callable by Fortran.
     (Some vendor-supplied BLAS libraries do not have C interfaces. So the 
      re-naming is needed in order for the SuperLU BLAS calls (in C) to 
      interface with the Fortran-style BLAS.)
     The possible options for CDEFS are:
         o -DAdd_: Fortran expects a C routine to have an underscore
           postfixed to the name;
         o -DNoChange: Fortran expects a C routine name to be identical to
               that compiled by C;
         o -DUpCase: Fortran expects a C routine name to be all uppercase.</p>
  
  <p>A Makefile is provided in each subdirectory. The installation can be done
  completely automatically by simply typing "make" at the top level.</p>
  
  <p>I am not really sure what this instruction means. Which of these three options should I choose? </p>