int main(void)
{
unsigned long i;
int isign;
float *data1,*data2,*fft1,*fft2;
data1=vector(1,N);
data2=vector(1,N);
fft1=vector(1,N2);
fft2=vector(1,N2);
for (i=1;i<=N;i++) {
data1[i]=floor(0.5+cos(i*2.0*PI/PER));
data2[i]=floor(0.5+sin(i*2.0*PI/PER));
}
twofft(data1,data2,fft1,fft2,N);
printf("Fourier transform of first function:\n");
prntft(fft1,N);
printf("Fourier transform of second function:\n");
prntft(fft2,N);
/* Invert transform */
isign = -1;
four1(fft1,N,isign);
printf("inverted transform = first function:\n");
prntft(fft1,N);
four1(fft2,N,isign);
printf("inverted transform = second function:\n");
prntft(fft2,N);
free_vector(fft2,1,N2);
free_vector(fft1,1,N2);
free_vector(data2,1,N);
free_vector(data1,1,N);
return 0;
}
void convlv(float data[], unsigned long n, float respns[], unsigned long m,
int isign, float ans[])
{
void realft(float data[], unsigned long n, int isign);
void twofft(float data1[], float data2[], float fft1[], float fft2[],
unsigned long n);
unsigned long i,no2;
float dum,mag2,*fft;
fft=vector(1,n<<1);
for (i=1;i<=(m-1)/2;i++)
respns[n+1-i]=respns[m+1-i];
for (i=(m+3)/2;i<=n-(m-1)/2;i++)
respns[i]=0.0;
twofft(data,respns,fft,ans,n);
no2=n>>1;
for (i=2;i<=n+2;i+=2) {
if (isign == 1) {
ans[i-1]=(fft[i-1]*(dum=ans[i-1])-fft[i]*ans[i])/no2;
ans[i]=(fft[i]*dum+fft[i-1]*ans[i])/no2;
} else if (isign == -1) {
if ((mag2=SQR(ans[i-1])+SQR(ans[i])) == 0.0)
nrerror("Deconvolving at response zero in convlv");
ans[i-1]=(fft[i-1]*(dum=ans[i-1])+fft[i]*ans[i])/mag2/no2;
ans[i]=(fft[i]*dum-fft[i-1]*ans[i])/mag2/no2;
} else nrerror("No meaning for isign in convlv");
}
ans[2]=ans[n+1];
realft(ans,n,-1);
free_vector(fft,1,n<<1);
}
void correl(real data1[],real data2[],int n,real ans[])
{
int no2,i;
real dum,*fft;
snew(fft,2*n+1);
twofft(data1,data2,fft,ans,n);
no2=n/2;
for (i=2;i<=n+2;i+=2) {
dum = ans[i-1];
ans[i-1] = (fft[i-1]*dum+fft[i]*ans[i])/no2;
ans[i] = (fft[i]*dum-fft[i-1]*ans[i])/no2;
}
ans[2]=ans[n+1];
realft(ans,no2,-1);
sfree(fft);
}
void correl(float data1[], float data2[], unsigned long n, float ans[])
{
void realft(float data[], unsigned long n, int isign);
void twofft(float data1[], float data2[], float fft1[], float fft2[],
unsigned long n);
unsigned long no2,i;
float dum,*fft;
fft=vector(1,n<<1);
twofft(data1,data2,fft,ans,n);
no2=n>>1;
for (i=2;i<=n+2;i+=2) {
ans[i-1]=(fft[i-1]*(dum=ans[i-1])+fft[i]*ans[i])/no2;
ans[i]=(fft[i]*dum-fft[i-1]*ans[i])/no2;
}
ans[2]=ans[n+1];
realft(ans,n,-1);
free_vector(fft,1,n<<1);
}
