Guru R2R Matrix Transposition

kml_fft_plan plan_transpose(int rows, int cols, double *in, double *out)
{
    const unsigned flags = KML_FFT_ESTIMATE;
    kml_fft_iodim howmany_dims[2];

    howmany_dims[0].n  = rows;
    howmany_dims[0].is = cols;
    howmany_dims[0].os = 1;

    howmany_dims[1].n  = cols;
    howmany_dims[1].is = 1;
    howmany_dims[1].os = rows;

    return kml_fft_plan_guru_r2r(/*rank=*/ 0, /*dims=*/ NULL,
                              /*howmany_rank=*/ 2, howmany_dims,
                              in, out, /*kind=*/ NULL, flags);
}
int main() {
    int len = 12;
    int rows = 3;
    int cols = 4;
    double *in = (double *)malloc(len * sizeof(double));
    for(int i = 0; i < len; i++) {
        in[i] = i;
    }
/*
 * 0 1 2 3
 * 4 5 6 7
 * 8 9 10 11
 */
    kml_fft_plan p = plan_transpose(rows, cols, in, in);
    kml_fft_execute(p);
/*
 * 0 4 8
 * 1 5 9
 * 2 6 10 
 * 3 7 11
 */
    free(in);
    kml_fft_destroy_plan(p);
}