try_fftw3.F90

! mac$ gfortran-mp-4.8 $(pkg-config --cflags --libs fftw3) try_fftw3.F90
! ubuntu$ gfortran $(pkg-config --cflags --libs fftw3) -I/usr/include try_fftw3.F90
! ubuntu$ ifort $(pkg-config --cflags --libs fftw3) try_fftw3.F90
program main
   use, intrinsic:: iso_fortran_env, only: INPUT_UNIT, OUTPUT_UNIT, ERROR_UNIT
   use, intrinsic:: iso_c_binding

   implicit none
   
   type(C_PTR):: plan
!   Integer(8):: plan
   Real(kind=C_DOUBLE):: in(1:128)
   Complex(kind=C_DOUBLE_COMPLEX):: out(1:128/2 + 1)
   Integer:: i

   include 'fftw3.f03'

   in = 0
   out = 0
!   call fftw_print_plan(fftw_plan_dft_r2c_1d(128_C_INT, in, out, FFTW_ESTIMATE))
   in = sin(0.1*[(i, i = 1, 128)])
   plan = fftw_plan_dft_r2c_1d(128_C_INT, in, out, FFTW_ESTIMATE)
   call fftw_execute_dft_r2c(plan, in, out)
!   call fftw_destroy_plan(plan)
!   do i = 1, 128
!      print*, in(i)
!   end do
   do i = 1, 128/2 + 1
      print*, abs(out(i))
   end do
!   print*, out

   stop
end program main