VAC PREPROCESSOR, as used for MPI-AMRVAC

This document briefly describes the use of the VAC PreProcessor (VACPP) which converts dimension independent notation into Fortran 90. VACPP is a specialized implementation of the general LASY Preprocessor.

VACPP is implemented in Perl in the src/vacpp.pl script. The main variables of VACPP, such as the number of dimensions $ndim and vector components $ndir, are normally modified by another Perl script src/setamrvac. Based on these variables and the LASY patterns in the *.t source files VACPP generates the Fortran 90 source code of the output *.f files.

The maximum length of the lines is determined by the final translation step and it can be set by the -maxlen=... flag. By default the output lines are at most 78 character long. Most compilers have flags to accept such line length, but if this is not the case, you may set '-maxlen=72' for the preprocessor step in src/makefile.

The preprocessor is mainly used via the makefile, but one can translate a single file directly, or even use the preprocessor interactively, when the dimension independent notation is typed in line by line from the keyboard and the expanded code appears on the screen. The interactive use is a very efficient way of checking the syntax of complex dimension independent notation. For interactive usage the number of dimensions and vector components can be overdefined temporarily with the -d flag. For example type (note the last dash!)

vacpp.pl -d=23 -
^D
1,2
^C
1,2,3
x(ixI^S,1)
x(ixImin1:ixImax1,ixImin2:ixImax2,1)
...
Ctrl-D

You may use vacpp.pl for translation directly

vacpp.pl FILENAME.t > FILENAME.f

or indirectly via the makefile with

make FILENAME.f

You may change the maximum line length to e.g. 72 directly on the command line

vacpp.pl -maxlen=72 FILENAME.t > FILENAME.f

or edit the src/makefile accordingly.