twofft.for

Numerical Recipes一书中例子的源码所用到的函数集,William H. Press 和 Saul A. Teukolsky 所著

      SUBROUTINE twofft(data1,data2,fft1,fft2,n)
      INTEGER n
      REAL data1(n),data2(n)
      COMPLEX fft1(n),fft2(n)
CU    USES four1
      INTEGER j,n2
      COMPLEX h1,h2,c1,c2
      c1=cmplx(0.5,0.0)
      c2=cmplx(0.0,-0.5)
      do 11 j=1,n
        fft1(j)=cmplx(data1(j),data2(j))
11    continue
      call four1(fft1,n,1)
      fft2(1)=cmplx(aimag(fft1(1)),0.0)
      fft1(1)=cmplx(real(fft1(1)),0.0)
      n2=n+2
      do 12 j=2,n/2+1
        h1=c1*(fft1(j)+conjg(fft1(n2-j)))
        h2=c2*(fft1(j)-conjg(fft1(n2-j)))
        fft1(j)=h1
        fft1(n2-j)=conjg(h1)
        fft2(j)=h2
        fft2(n2-j)=conjg(h2)
12    continue
      return
      END