code: def sigtdAngle(self,dangle):
          
          Tlow= dangle/(self._meandO+3.*numpy.sqrt(self._sortedSigOEig[2]))
          Thigh= dangle/(self._meandO-3.*numpy.sqrt(self._sortedSigOEig[2]))
          numsig2= integrate.quad(lambda x: x**2.*self.ptdAngle(x,dangle),
                                  Tlow,Thigh)[0]
          nummean= integrate.quad(lambda x: x*self.ptdAngle(x,dangle),
                                  Tlow,Thigh)[0]
          denom= integrate.quad(self.ptdAngle,Tlow,Thigh,(dangle,))[0]
          if denom == 0.: return numpy.nan
          else: return numpy.sqrt(numsig2/denom-(nummean/denom)**2.)
docs: NAME:
  
             sigtdAngle
  
          PURPOSE:
  
             calculate the dispersion in the stripping times at a given angle
  
          INPUT:
  
             dangle - angle offset along the stream
  
          OUTPUT:
  
             dispersion in the stripping times at this angle
  
          HISTORY:
  
             2013-12-05 - Written - Bovy (IAS)