在 R 中使用 Fortran 子程序？错误：返回类型不匹配

Question

我正在尝试学习如何在 R 中使用 fortran 代码。我能够关注 this tutorial。现在，我正在尝试将其用作基础加上this fortran program to calculate pi。我用这段代码创建了一个文件 Fpi.f90：

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

! we set it to zero in the sequential run
rank = 0
! initialize the random number generator
! we make sure the seed is different for 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
do i = 0, ROUNDS-1
  pi_est = dboard(DARTS)
  ! calculate the average value of pi over all iterations
  avepi = ((avepi*i) + pi_est)/(i + 1)
end do
end subroutine pi


double precision function dboard(darts)
integer, intent(in)           :: darts
double precision              :: x_coord, y_coord
integer                       :: score, n

score = 0
do n = 1, darts
  call random_number(x_coord)
  call random_number(y_coord)

  if ((x_coord**2 + y_coord**2) <= 1.0d0) then
  score = score + 1
  end if
end do
dboard = 4.0d0*score/darts

end function

什么时候

$ R CMD SHLIB ./Fortran/Fpi.f90
gfortran  -fpic -g -O2 -fstack-protector-strong  -c  Fortran/Fpi.f90 -o Fortran/Fpi.o
Fortran/Fpi.f90:22.15:

pi_est = dboard(DARTS)
               1
Error: Return type mismatch of function 'dboard' at (1) (REAL(4)/REAL(8))
/usr/lib/R/etc/Makeconf:161: recipe for target 'Fortran/Fpi.o' failed
make: *** [Fortran/Fpi.o] Error 1

我做错了什么？

---

将double precision :: dboard 添加到pi 后，我得到一个不同的错误。

R CMD SHLIB ./Fortran/Fpi.f90
gfortran -shared -L/usr/lib/R/lib -Wl,-z,relro -o Fortran/Fpi.so ./Fortran/Fpi.o -L/usr/lib/R/lib -lR
/usr/bin/ld: ./Fortran/Fpi.o: relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; recompile with -fPIC
./Fortran/Fpi.o: error adding symbols: Bad value
collect2: error: ld returned 1 exit status
/usr/share/R/share/make/shlib.mk:6: recipe for target 'Fortran/Fpi.so' failed
make: *** [Fortran/Fpi.so] Error 1

Answer 1

您不使用implicit none。这是非常糟糕的！由于隐式键入 dboard 被认为是他在 pi 中的默认真实值。

将其声明为双精度，或者如果可能使用 R，请使用模块。接口块也可用于在pi 中声明dboard。