twoff.cpp

此程序为VC++常用数值算法这本书附赠的光盘中包含了本书中全部的源代码

void twofft(double data1[], double data2[], double fft1[],
			double fft2[], int& n)
{
	int j,n2,j2;
	double c1r,c1i,c2r,c2i,conjr,conji,h1r,h1i,h2r,h2i;
    c1r = 0.5;
    c1i = 0.0;
    c2r = 0.0;
    c2i = -0.5;
    for (j = 1; j<=n; j++)
	{
        fft1[2 * j - 1] = data1[j];
        fft1[2 * j] = data2[j];
    }
    four1(fft1, n, 1);
    fft2[1] = fft1[2];
    fft2[2] = 0.0;
    fft1[2] = 0.0;
    n2 = 2 * (n + 2);
    for (j = 2; j<=n / 2 + 1; j++)
	{
        j2 = 2 * j;
        conjr = fft1[n2 - j2 - 1];
        conji = -fft1[n2 - j2];
        h1r=c1r*(fft1[j2-1]+conjr)-c1i*(fft1[j2]+conji);
        h1i=c1i*(fft1[j2-1]+conjr)+c1r*(fft1[j2]+conji);
        h2r=c2r*(fft1[j2-1]-conjr)-c2i*(fft1[j2]-conji);
        h2i=c2i*(fft1[j2-1]-conjr)+c2r*(fft1[j2]-conji);
        fft1[j2 - 1] = h1r;
        fft1[j2] = h1i;
        fft1[n2 - j2 - 1] = h1r;
        fft1[n2 - j2] = -h1i;
        fft2[j2 - 1] = h2r;
        fft2[j2] = h2i;
        fft2[n2 - j2 - 1] = h2r;
        fft2[n2 - j2] = -h2i;
    }
}