Use Fortran subroutine in R? Undefined symbol -

this follow to previous question. wrapped fortran code in module , compiles when run:

r cmd shlib ./fortran/fpi.f90 

this fortran code:

module fpi  implicit none contains      subroutine pi(avepi, darts, rounds)     double precision, intent(out)   ::  avepi     integer, intent(in)             ::  darts, rounds     integer                         ::  master, rank, i, n     integer, allocatable            ::  seed(:)     double precision                ::  pi_est, homepi, pirecv, pisum, dboard      ! set 0 in sequential run     rank = 0     ! initialize random number generator     ! make sure seed different each task     call random_seed()     call random_seed(size = n)     allocate(seed(n))     seed = 12 + rank*11     call random_seed(put=seed(1:n))     deallocate(seed)      avepi = 0     = 0, rounds-1       pi_est = dboard(darts)       ! calculate average value of pi on iterations       avepi = ((avepi*i) + pi_est)/(i + 1)     end     end subroutine pi       double precision function dboard(darts)     integer, intent(in)           :: darts     double precision              :: x_coord, y_coord     integer                       :: score, n      score = 0     n = 1, darts       call random_number(x_coord)       call random_number(y_coord)        if ((x_coord**2 + y_coord**2) <= 1.0d0)       score = score + 1       end if     end     dboard = 4.0d0*score/darts      end function   end module fpi  

i'm trying run in r:

mypi <- function(darts, rounds) {   dyn.load("./fortran/fpi.so")   retvals <- .fortran("pi", darts = as.integer(darts) , rounds = as.integer(rounds), avepi = as.numeric(1))   return(retvals$avepi) }  mypi(darts = 50000, rounds = 10) 

and error:

error in dyn.load("./fortran/fpi.so") :    unable load shared object '/home/ignacio/local/projects/pi/./fortran/fpi.so':   /home/ignacio/local/projects/pi/./fortran/fpi.so: undefined symbol: dboard_ 

your problem comes down declaration of dboard:

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

here saying dboard external function, rather module procedure. explains why there symbol dboard_ coming play. want remove that:

double precision                ::  pi_est, homepi, pirecv, pisum 

and instead rely, in pi on module procedure-ness of dboard: pi knows without declaration.

now, beyond that, because pi in module there going name mangling going on subroutine itself. i'd solve problem making pi (c) interoperable procedure.

module fpi    implicit none contains    subroutine pi(avepi, darts, rounds) bind(c)     use, intrinsic :: iso_c_binding, : c_double, c_int     real(c_double), intent(out)   ::  avepi     integer(c_int), intent(in)    ::  darts, rounds     ... 

and using .c rather .fortran.

you can keep pi , dboard in module, , latter needn't interoperable.