fftw-1d.c

这是一个实用的并行计算源代码

#include "fftw3.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define N	4
#define REAL	0
#define IMAG	1
#define PI	3.1415926535898

int main (void)
{
    fftw_complex *in, *out;
    fftw_plan p;
    double constants[N] = {10, 2.1, 4.7, 1.3};
    double f;
    int i, j;

    /* Allocate memory for the arrays */
    in = fftw_malloc(sizeof(fftw_complex) * N);
    out = fftw_malloc(sizeof(fftw_complex) * N);

    if ((in == NULL) || (out == NULL)) {
	printf ("Error: insufficient available memory\n");
    }
    else {
	/* Create the FFTW execution plan */
	p = fftw_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);

	/* Initialize the input data */
	for (i = 0; i < N; i++) { /* All sampling points */
	    in[i][REAL] = constants[0];
	    in[i][IMAG] = 0;
	    for (j = 1; j < N; j++) { /* All frequencies */
		in[i][REAL] += constants[j] * cos(j * i * 2 * PI / (double)N);
		in[i][IMAG] += constants[j] * sin(j * i * 2 * PI / (double)N);
	    }
	}

	/* Execute plan */
	fftw_execute(p);

	/* Destroy plan */
	fftw_destroy_plan(p);

	/* Display results */
	printf ("Constants[] = {");
	for (i = 0; i < N; i++)
	    printf("%lf%s", constants[i], (i == N-1) ? "}\n" : ", ");

	printf ("Input[][REAL] = {");
	for (i = 0; i < N; i++)
	    printf("%lf%s", in[i][REAL], (i == N-1) ? "}\n" : ", ");

	printf ("Output[][REAL] = {");
	for (i = 0; i < N; i++)
	    printf("%lf%s", out[i][REAL], (i == N-1) ? "}\n" : ", ");

	/* Scale output */
	f = 1.0/sqrt((double)N);
	for (i = 0; i < N; i++)
	    out[i][REAL] *= f;

	/* Display final results */
	printf ("Scaled[][REAL] = {");
	for (i = 0; i < N; i++)
	    printf("%lf%s", out[i][REAL], (i == N-1) ? "}\n" : ", "); 
    }

    /* Free allocated memory */
    if (in != NULL) fftw_free(in);
    if (out != NULL) fftw_free(out);

    return 0;
}