code: def Rphideriv(self,R,Z,phi=0.,t=0.):
          
          try:
              return self._amp*self._Rphideriv(R,Z,phi=phi,t=t)
          except AttributeError: #pragma: no cover
              if self.isNonAxi:
                  raise PotentialError("'_phiforce' function not implemented for this non-axisymmetric potential")
              return 0.
docs: NAME:
  
             Rphideriv
  
          PURPOSE:
  
             evaluate the mixed radial, azimuthal derivative
  
          INPUT:
  
             R - Galactocentric radius (can be Quantity)
  
             Z - vertical height (can be Quantity)
  
             phi - Galactocentric azimuth (can be Quantity)
  
             t - time (can be Quantity)
  
          OUTPUT:
  
             d2Phi/dphidR
  
          HISTORY:
  
             2014-06-30 - Written - Bovy (IAS)