code: def get_kx(N,dx):
      
      
      # to work with dimensional axes
      L = N*dx
      
      #Odd or even
      odd = N&1 and True or False
      
      #Get frequency & wavenumber
      k=ft.fftfreq(N,d=dx)
  #    k=f*N
      
      imx = (N-1)/2 if odd else N/2 #Maximum frequency
      
      #Convert into frequencies
  #    k/=L
      
      return k, L, imx
docs: GET_KX
      :summary: Returns the frequencies to be used with FFT analysis
      
      :parameter N: number of samples in data
      :parameter dx: sampling step
      
      :return: Returns
        * k: frequency
        * L: length
        * imx: index of maximum frequency (for separating positive and negative frequencies)
      
      :author: Renaud DUSSURGET (RD) - LER/PAC, Ifremer
      :change: Created by RD, July 2012