Calling METIS API(wrtten in C language) in fortran program

Question

Over 2 weeks, I\'ve struggled to call one of the METIS library written in C from my fortran code. And, unfortunately, It doesn\'t seem to be a HAPPY END without your help. I

Answer 1

I think your opts(7) does not work because you also need an interface for the METIS function METIS_SetDefaultOptions. Based on the answer from http://glaros.dtc.umn.edu/gkhome/node/877, I created a wrapper module (metisInterface.F90) with the interfaces I needed:

module metisInterface
! module to allows us to call METIS C functions from the main Fortran code

   use,intrinsic :: ISO_C_BINDING

   integer :: ia,ic
   integer(C_INT) :: metis_ne,metis_nn
   integer(C_INT) :: ncommon,objval
   integer(C_INT) :: nparts
   integer(C_INT),allocatable,dimension(:) :: eptr,eind,perm,iperm
   integer(C_INT),allocatable,dimension(:) :: epart,npart
   type(C_PTR) :: vwgt,vsize,twgts,tpwgts
   integer(C_INT) :: opts(0:40)


   interface
      integer(C_INT) function METIS_SetDefaultOptions(opts) bind(C,name="METIS_SetDefaultOptions")
         use,intrinsic :: ISO_C_BINDING
         implicit none
         integer(C_INT) :: opts(0:40)
      end function METIS_SetDefaultOptions
   end interface 

   interface
      integer(C_INT) function METIS_PartMeshDual(ne,nn,eptr,eind,vwgt,vsize,ncommon,nparts,tpwgts, &
                              opts,objval,epart,npart) bind(C,name="METIS_PartMeshDual")
         use,intrinsic :: ISO_C_BINDING
         implicit none
         integer(C_INT):: ne, nn
         integer(C_INT):: ncommon, objval
         integer(C_INT):: nparts
         integer(C_INT),dimension(*) :: eptr, eind
         integer(C_INT),dimension(*) :: epart, npart
         type(C_PTR),value :: vwgt, vsize, tpwgts
         integer(C_INT) :: opts(0:40)
      end function METIS_PartMeshDual
   end interface    

end module metisInterface

Then, in the main program (or wherever you make the call to the METIS functions) you need to have (for completeness, I also added the call to METIS_PartMeshDual):

use metisInterface

integer :: metis_call_status
.
.
.
metis_call_status = METIS_SetDefaultOptions(opts)

! METIS_OPTION_NUMBERING for Fortran
opts(17) = 1

metis_call_status = METIS_PartMeshDual(metis_ne,metis_nn,eptr,eind, &
                    vwgt,vsize,ncommon,nparts,tpwgts,opts,objval,epart,npart)

Note that epart and npart will have Fortran numbering as you want (starting at 1). However, the processors will also start numbering at 1. For example, if you are running in 4 processors, root processor is 1 and you may have epart(n)=4, and you will not have any epart(n)=0.

Finally, a file metis.c is also needed with a single line:

#include "metis.h"

Compiling instructions

1. Compile metis.c with a C compiler
2. Compile metisInterface.F90 with a Fortran compiler linking with the compiled C object
3. Compile main program with a Fortran compiler linking with metisInterface.o