xfour1.c

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/* Driver for routine four1 */

#include <stdio.h>
#include <math.h>
#define NRANSI
#include "nr.h"
#include "nrutil.h"

void prntft(float data[],unsigned long nn)
{
	unsigned long n;

	printf("%4s %13s %13s %12s %13s\n",
		"n","real(n)","imag.(n)","real(N-n)","imag.(N-n)");
	printf("   0 %14.6f %12.6f %12.6f %12.6f\n",
		data[1],data[2],data[1],data[2]);
	for (n=3;n<=nn+1;n+=2) {
		printf("%4lu %14.6f %12.6f %12.6f %12.6f\n",
			((n-1)/2),data[n],data[n+1],
			data[2*nn+2-n],data[2*nn+3-n]);
	}
	printf(" press return to continue ...\n");
	(void) getchar();
	return;
}

#define NN 32
#define NN2 (2*NN)

int main(void)
{
	long i;
	int isign;
	float *data,*dcmp;

	data=vector(1,NN2);
	dcmp=vector(1,NN2);
	printf("h(t)=real-valued even-function\n");
	printf("h(n)=h(N-n) and real?\n");
	for (i=1;i<NN2;i+=2) {
		data[i]=1.0/(SQR((float) (i-NN-1)/NN)+1.0);
		data[i+1]=0.0;
	}
	isign=1;
	four1(data,NN,isign);
	prntft(data,NN);
	printf("h(t)=imaginary-valued even-function\n");
	printf("h(n)=h(N-n) and imaginary?\n");
	for (i=1;i<NN2;i+=2) {
		data[i+1]=1.0/(SQR((float) (i-NN-1)/NN)+1.0);
		data[i]=0.0;
	}
	isign=1;
	four1(data,NN,isign);
	prntft(data,NN);
	printf("h(t)=real-valued odd-function\n");
	printf("h(n) = -h(N-n) and imaginary?\n");
	for (i=1;i<NN2;i+=2) {
		data[i]=((float) (i-NN-1)/NN)/(SQR((float) (i-NN-1)/NN)+1.0);
		data[i+1]=0.0;
	}
	data[1]=0.0;
	isign=1;
	four1(data,NN,isign);
	prntft(data,NN);
	printf("h(t)=imaginary-valued odd-function\n");
	printf("h(n) = -h(N-n) and real?\n");
	for (i=1;i<NN2;i+=2) {
		data[i+1]=((float) (i-NN-1)/NN)/(SQR((float) (i-NN-1)/NN)+1.0);
		data[i]=0.0;
	}
	data[2]=0.0;
	isign=1;
	four1(data,NN,isign);
	prntft(data,NN);
	/* transform, inverse-transform test */
	for (i=1;i<NN2;i+=2) {
		data[i]=1.0/(SQR(0.5*(i-NN-1.0)/NN)+1.0);
		dcmp[i]=data[i];
		data[i+1]=(0.25*(i-NN-1.0)/NN)*exp(-SQR(0.5*(i-NN-1)/NN));
		dcmp[i+1]=data[i+1];
	}
	isign=1;
	four1(data,NN,isign);
	isign = -1;
	four1(data,NN,isign);
	printf("%23s %33s \n","original data:","double fourier transform:");
	printf("\n %3s %15s %12s %12s %12s \n",
		"k","real h(k)","imag h(k)","real h(k)","imag h(k)");
	for (i=1;i<NN;i+=2)
		printf("%4lu %14.6f %12.6f %12.6f %12.6f\n",
			(i+1)/2,dcmp[i],dcmp[i+1],data[i]/NN,data[i+1]/NN);
	free_vector(dcmp,1,NN2);
	free_vector(data,1,NN2);
	return 0;
}
#undef NRANSI