code: def epifreq(Pot,R):
      
      from .planarPotential import planarPotential
      if isinstance(Pot,(Potential,planarPotential)):
          return Pot.epifreq(R,use_physical=False)
      from galpy.potential import evaluateplanarRforces, evaluateplanarR2derivs
      from galpy.potential import PotentialError
      try:
          return nu.sqrt(evaluateplanarR2derivs(Pot,R,use_physical=False)
                         -3./R*evaluateplanarRforces(Pot,R,use_physical=False))
      except PotentialError:
          from galpy.potential import RZToplanarPotential
          Pot= RZToplanarPotential(Pot)
          return nu.sqrt(evaluateplanarR2derivs(Pot,R,use_physical=False)
                         -3./R*evaluateplanarRforces(Pot,R,use_physical=False))
docs: NAME:
      
          epifreq
      
      PURPOSE:
      
          calculate the epicycle frequency at R in the potential Pot
      
      INPUT:
  
          Pot - Potential instance or list thereof
      
          R - Galactocentric radius (can be Quantity)
      
      OUTPUT:
      
          epicycle frequency
      
      HISTORY:
      
          2012-07-25 - Written - Bovy (IAS)