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PROGRAM test
use, intrinsic :: iso_c_binding
IMPLICIT none
INCLUDE 'fftw3.f03'
integer, parameter :: npoints = 1024
real(C_DOUBLE), parameter :: start = 0, end = 1
integer :: i
real(C_DOUBLE) :: t, &
delta = (end - start) / real(npoints - 1, C_DOUBLE)
type(C_PTR) :: p_in!, p_out, plan
real(C_DOUBLE), pointer :: arr_in(:)
! complex(C_DOUBLE_COMPLEX), pointer :: out_arr(npoints)
p_in = fftw_alloc_real(int(npoints, C_SIZE_T))
call c_f_pointer(p_in, arr_in, [npoints])
DO i = 1, npoints
t = (i - 1) * delta + start
arr_in(i) = f1(t)
write(*,*) t, " ", arr_in(i)
END DO
call fftw_free(p_in)
CONTAINS
PURE real(C_DOUBLE) FUNCTION f1(t)
real(C_DOUBLE), intent(in) :: t
real(C_DOUBLE), parameter :: pi = acos(-1.0)
f1 = sin(2 * pi * t * 200) + 2 * sin(2 * pi * t * 400)
END FUNCTION f1
END PROGRAM test
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