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add numerical recipes library

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yenru0
2025-09-12 18:55:25 +09:00
parent d4dff245bd
commit 2c75620ec9
1344 changed files with 63869 additions and 0 deletions
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32
lib/nr/k_and_r/recipes/twofft.c Normal file
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void twofft(data1,data2,fft1,fft2,n)
float data1[],data2[],fft1[],fft2[];
unsigned long n;
{
void four1();
unsigned long nn3,nn2,jj,j;
float rep,rem,aip,aim;
nn3=1+(nn2=2+n+n);
for (j=1,jj=2;j<=n;j++,jj+=2) {
fft1[jj-1]=data1[j];
fft1[jj]=data2[j];
}
four1(fft1,n,1);
fft2[1]=fft1[2];
fft1[2]=fft2[2]=0.0;
for (j=3;j<=n+1;j+=2) {
rep=0.5*(fft1[j]+fft1[nn2-j]);
rem=0.5*(fft1[j]-fft1[nn2-j]);
aip=0.5*(fft1[j+1]+fft1[nn3-j]);
aim=0.5*(fft1[j+1]-fft1[nn3-j]);
fft1[j]=rep;
fft1[j+1]=aim;
fft1[nn2-j]=rep;
fft1[nn3-j] = -aim;
fft2[j]=aip;
fft2[j+1] = -rem;
fft2[nn2-j]=aip;
fft2[nn3-j]=rem;
}
}