code: def calcRapRperi(self,*args,**kwargs):
          
          #Set up the actionAngleAxi object
          if isinstance(self._pot,list):
              thispot= [p.toPlanar() for p in self._pot if not isinstance(p,planarPotential)]
              thispot.extend([p for p in self._pot if isinstance(p,planarPotential)])
          elif not isinstance(self._pot,planarPotential):
              thispot= self._pot.toPlanar()
          else:
              thispot= self._pot
          aAAxi= actionAngleAxi(*args,pot=thispot,
                                 gamma=self._gamma)
          return aAAxi.calcRapRperi(**kwargs)
docs: NAME:
             calcRapRperi
          PURPOSE:
             calculate the apocenter and pericenter radii
          INPUT:
             Either:
                a) R,vR,vT,z,vz
                b) Orbit instance: initial condition used if that's it, orbit(t)
                   if there is a time given as well
          OUTPUT:
             (rperi,rap)
          HISTORY:
             2013-11-27 - Written - Bovy (IAS)