kml_fft(f)_plan_dft_r2c

Create a plan for the n-dimensional real-to-complex (R2C) transform of a single contiguous data sequence.

Interface Definition

C interface:

kml_fft_plan kml_fft_plan_dft_r2c(int rank, const int *n, double *in, kml_fft_complex *out, unsigned flags);

kml_fftf_plan kml_fftf_plan_dft_r2c(int rank, const int *n, float *in, kml_fftf_complex *out, unsigned flags);

Fortran interface:

RES = KML_FFT_PLAN_DFT_R2C(RANK, N, IN, OUT, FLAGS);

RES = KML_FFTF_PLAN_DFT_R2C(RANK, N, IN, OUT, FLAGS);

Return Value

The function returns a structure pointer of the kml_fft(f)_plan type. This object is used as a parameter in the kml_fft(f)_execute function to perform FFT on the current input and output. In addition, the object may also be added into the kml_fft(f)_execute_dft_r2c function as a parameter to perform FFT on the new input and output.

If this function returns a non-null pointer, the plan has been successfully executed. Otherwise, the plan failed to be executed.

Parameters

Parameter	Data Type	Description	Input/Output
rank	int	Dimension of FFT. The constraint is 1 <= rank <= 3.	Input
n	const int*	Indicates an array whose dimension is rank, including the size of each dimension in the FFT sequence. The constraint is n[i] >= 1, for i in 0 to rank - 1.	Input
in	Double precision: double* Single precision: float*	Inputs the data to be transformed.	Input
out	Double precision: kml_fft_complex* Single precision: kml_fftf_complex*	Outputs the data generated using FFT.	Output
flags	unsigned int	A planning option, not in use.	Input

Dependencies

C: "kfft.h"

Fortran: "kfft.f03"

Examples

C interface:

    int rank = 2; 
    int *n; 
    n = (int*)kml_fft_malloc(sizeof(int) * rank); 
    n[0] = 2; 
    n[1] = 4; 
    double init[8] = {1, 2, 3, 4, 5, 6, 7, 8}; 
    double *in; 
    in = (double*)kml_fft_malloc(sizeof(double) * n[0] * n[1]); 
    for (int i = 0; i < n[0] * n[1]; i++) { 
        in[i] = init[i]; 
    } 
    kml_fft_complex *out; 
    out = (kml_fft_complex*)kml_fft_malloc(sizeof(kml_fft_complex) * n[0] * (n[1] / 2 + 1)); 
    kml_fft_plan plan; 
    plan = kml_fft_plan_dft_r2c(rank, n, in, out, KML_FFT_ESTIMATE); 
    kml_fft_execute_dft_r2c(plan, in, out); 
 
    kml_fft_destroy_plan(plan); 
    kml_fft_free(n); 
    kml_fft_free(in); 
    kml_fft_free(out); 
 
    /* 
     * out = {{3.600000e+01, 0.000000e+00}, {-4.000000e+00, 4.000000e+00}, 
     *        {-4.000000e+00, 0.000000e+00}, {-1.600000e+01, 0.000000e+00}, 
     *        {0.000000e+00, 0.000000e+00}, {0.000000e+00, 0.000000e+00}} 
     */

Fortran interface:

    INTEGER(C_INT) :: RANK = 2 
    INTEGER(C_INT) :: N(2) 
    REAL(C_DOUBLE) :: INIT(8)  
    REAL(C_DOUBLE), POINTER :: IN 
    TYPE(KML_FFT_COMPLEX), POINTER :: OUT 
    TYPE(C_PTR) :: PIN, POUT 
    INTEGER(C_SIZE_T) :: RSIZE, CSIZE 
    RSIZE = N(1) * N(2) 
    CSIZE = N(1) * (N(2) / 2 + 1) 
    PIN = KML_FFT_MALLOC(8 * RSIZE) 
    POUT = KML_FFT_MALLOC(16 * CSIZE) 
    CALL C_F_POINTER(PIN, IN, SHAPE=[RSIZE]) 
    CALL C_F_POINTER(POUT, OUT, SHAPE=[CSIZE]) 
    DATA N/2, 4/ 
    DATA INIT/1, 2, 3, 4, 5, 6, 7, 8/ 
    INTEGER :: I 
    DO WHILE(I <= RSIZE) 
        IN(I) = INIT(I) 
    END DO 
     
    TYPE(C_PTR) :: PLAN 
    PLAN = KML_FFT_PLAN_DFT_R2C(RANK, N, IN, OUT, KML_FFT_ESTIMATE) 
    CALL KML_FFT_EXECUTE_DFT_R2C(PLAN, IN, OUT) 
 
    CALL KML_FFT_DESTROY_PLAN(PLAN) 
    CALL KML_FFT_FREE(PIN) 
    CALL KML_FFT_FREE(POUT) 
 
    ! 
    ! OUT = /3.600000E+01, 0.000000E+00, -4.000000E+00, 4.000000E+00, 
    !        -4.000000E+00, 0.000000E+00, -1.600000E+01, 0.000000E+00, 
    !        0.000000E+00, 0.000000E+00, 0.000000E+00, 0.000000E+00/ 
    !

Parent topic: R2C Transforms