code: def _xw(self,*args,**kwargs): #pragma: no cover
          
          #BOVY: REPLACE WITH CALCULATION FUNCTION
          x= self.x(self.t)
          xw= nu.fft.fft(x)#-nu.mean(x))
          xw= nu.abs(xw[0:len(xw)/2])*(self.t[1]-self.t[0])/(self.t[-1]-self.t[0])
          return xw
docs: NAME:
             xw
          PURPOSE:
             return the Fourier transform of xx
          INPUT:
             t - (optional) time at which to get xw
          OUTPUT:
             xw(t)
          HISTORY:
             2011-01-04 - Written - Bovy (NYU)