program slowft
c     Fourier Transform
c     time (x) in atomic units
      implicit none
      real*8 t,y,wmin,wmax,delw,arg,pi,w
      integer*4 n,nw,iw,iargc
      character*80 st,fi,fo
      real*8,allocatable::s(:),c(:)
      pi=4.0d0*atan(1.0d0)
      if(iargc().ne.5)then
       write(6,*)'Usage wmin wmax delw <input file> <output file>'
      else
       call getarg(1,st)
       read(st,*)wmin
       call getarg(2,st)
       read(st,*)wmax
       call getarg(3,st)
       read(st,*)delw
       call getarg(4,fi)
       call getarg(5,fo)
       nw=NINT((wmax-wmin)/delw)+1
       allocate(s(nw),c(nw))
       do 4 iw=1,nw
       s(iw)=0.0d0
4      c(iw)=0.0d0
       n=0
       open(9,file=fi)
1      read(9,*,end=99,err=99)t,y
c      atomic units to fs
       t=t/41.3413745758d0
       w=wmin-delw
       do 2 iw=1,nw
       w=w+delw
       arg=2.0d0*pi*w*t*3.0d10*1.0d-15
       s(iw)=s(iw)+y*sin(arg)
2      c(iw)=c(iw)+y*cos(arg)
       n=n+1
       goto 1
99     close(9)
       write(6,*)n,' points'
       if(n.gt.0)then
        open(9,file=fo)
        w=wmin-delw
        do 3 iw=1,nw
        w=w+delw
3       write(9,900)w,s(iw)**2+c(iw)**2
900     format(2g15.6)
        close(9)
       endif
      endif
      end