Use Fortran subroutine in R? Undefined symbol

Question

This is a follow up to my previous question. I wrapped my Fortran code in a module and now it compiles when I run:

R CMD SHLIB ./Fortran/Fpi.f90

Answer 1

Your problem comes down to the declaration of dboard:

   double precision                ::  pi_est, homepi, pirecv, pisum, dboard

Here you are saying that dboard is an external function, rather than a module procedure. This explains why there is a symbol dboard_ coming into play. You want to remove that:

double precision                ::  pi_est, homepi, pirecv, pisum

and instead rely, in pi on the module procedure-ness of dboard: pi already knows about it without this declaration.

Now, beyond that, because pi is in a module there is going to be some name mangling going on for that subroutine itself. I'd solve this problem by making pi itself a (C) interoperable procedure.

Module Fpi 
  IMPLICIT NONE
contains 
  subroutine pi(avepi, DARTS, ROUNDS) bind(C)
    use, intrinsic :: iso_c_binding, only : c_double, c_int
    real(c_double), intent(out)   ::  avepi
    integer(c_int), intent(in)    ::  DARTS, ROUNDS
    ...

and then using .C rather than .Fortran.

You can keep pi and dboard in the module, and this latter needn't even be interoperable.