code: def evaluateR2derivs(Pot,R,z,phi=None,t=0.):
      
      isList= isinstance(Pot,list)
      nonAxi= _isNonAxi(Pot)
      if nonAxi and phi is None:
          raise PotentialError("The (list of) Potential instances is non-axisymmetric, but you did not provide phi")
      if isList:
          sum= 0.
          for pot in Pot:
              if not isinstance(pot,DissipativeForce):
                  sum+= pot.R2deriv(R,z,phi=phi,t=t,use_physical=False)
          return sum
      elif isinstance(Pot,Potential):
          return Pot.R2deriv(R,z,phi=phi,t=t,use_physical=False)
      else: #pragma: no cover 
          raise PotentialError("Input to 'evaluateR2derivs' is neither a Potential-instance or a list of such instances")
docs: NAME:
  
         evaluateR2derivs
  
      PURPOSE:
  
         convenience function to evaluate a possible sum of potentials
  
      INPUT:
  
         Pot - a potential or list of potentials (dissipative forces in such a list are ignored)
  
         R - cylindrical Galactocentric distance (can be Quantity)
  
         z - distance above the plane (can be Quantity)
  
         phi - azimuth (optional; can be Quantity)
  
         t - time (optional; can be Quantity)
  
      OUTPUT:
  
         d2Phi/d2R(R,z,phi,t)
  
      HISTORY:
  
         2012-07-25 - Written - Bovy (IAS)