code: def TR(self,**kwargs): #pragma: no cover
          
          if hasattr(self,'_TR'):
              return self._TR
          (rperi,rap)= self.calcRapRperi(**kwargs)
          if nu.fabs(rap-rperi)/rap < 10.**-4.: #Rough limit
              self._TR= 2.*m.pi/epifreq(self._pot,self._R,use_physical=False)
              return self._TR
          Rmean= m.exp((m.log(rperi)+m.log(rap))/2.)
          EL= self.calcEL(**kwargs)
          E, L= EL
          TR= 0.
          if Rmean > rperi:
              TR+= integrate.quadrature(_TRAxiIntegrandSmall,
                                        0.,m.sqrt(Rmean-rperi),
                                        args=(E,L,self._pot,rperi),
                                        **kwargs)[0]
          if Rmean < rap:
              TR+= integrate.quadrature(_TRAxiIntegrandLarge,
                                        0.,m.sqrt(rap-Rmean),
                                        args=(E,L,self._pot,rap),
                                        **kwargs)[0]
          self._TR= 2.*TR
          return self._TR
docs: NAME:
             TR
          PURPOSE:
             Calculate the radial period for a power-law rotation curve
          INPUT:
             scipy.integrate.quadrature keywords
          OUTPUT:
             T_R(R,vT,vT)*vc/ro + estimate of the error
          HISTORY:
             2010-12-01 - Written - Bovy (NYU)