def E(self,*args,**kwargs):
        """
        NAME:
           E
        PURPOSE:
           calculate the energy
        INPUT:
           t - (optional) time at which to get the radius
           pot= potential instance or list of such instances
        OUTPUT:
           energy
        HISTORY:
           2010-09-15 - Written - Bovy (NYU)
           2011-04-18 - Added t - Bovy (NYU)
        """
        if not 'pot' in kwargs or kwargs['pot'] is None:
            try:
                pot= self._pot
            except AttributeError:
                raise AttributeError("Integrate orbit or specify pot=")
            if 'pot' in kwargs and kwargs['pot'] is None:
                kwargs.pop('pot')          
        else:
            pot= kwargs.pop('pot')
        if isinstance(pot,Potential):
            thispot= RZToplanarPotential(pot)
        elif isinstance(pot,list):
            thispot= []
            for p in pot:
                if isinstance(p,Potential): thispot.append(RZToplanarPotential(p))
                else: thispot.append(p)
        else:
            thispot= pot
        if len(args) > 0:
            t= args[0]
        else:
            t= 0.
        #Get orbit
        thiso= self(*args,**kwargs)
        onet= (len(thiso.shape) == 1)
        if onet:
            return _evaluateplanarPotentials(thispot,thiso[0],
                                             t=t)\
                                            +thiso[1]**2./2.\
                                            +thiso[2]**2./2.
        else:
            return nu.array([_evaluateplanarPotentials(thispot,thiso[0,ii],
                                                      t=t[ii])\
                                 +thiso[1,ii]**2./2.\
                                 +thiso[2,ii]**2./2. for ii in range(len(t))])
NAME:
           E
        PURPOSE:
           calculate the energy
        INPUT:
           t - (optional) time at which to get the radius
           pot= potential instance or list of such instances
        OUTPUT:
           energy
        HISTORY:
           2010-09-15 - Written - Bovy (NYU)
           2011-04-18 - Added t - Bovy (NYU)