code: def _ELtowRRapRperi(self,E,L):
          
          if self._beta == 0.:
              xE= sc.exp(E-.5)
          else: #non-flat rotation curve                                      
              xE= (2.*E/(1.+1./self._beta))**(1./2./self._beta)
          rperi,rap= self._aA.calcRapRperi(xE,0.,L/xE,0.,0.)
          #Replace the above w/
          aA= actionAngleAxi(xE,0.,L/xE,
                             pot=PowerSphericalPotential(normalize=1.,
                                                         alpha=2.-2.*self._beta).toPlanar())
          TR= aA.TR()
          return (2.*math.pi/TR,rap,rperi)
docs: NAME:
             _ELtowRRapRperi
          PURPOSE:
             calculate the radial frequency based on E,L, also return rap and 
             rperi
          INPUT:
             E - energy
             L - angular momentum
          OUTPUT:
             wR(E.L)
          HISTORY:
             2010-07-11 - Written - Bovy (NYU)