code: def flattening(Pot,R,z):
      
      return nu.sqrt(nu.fabs(z/R*evaluateRforces(Pot,R,z,use_physical=False)\
                                 /evaluatezforces(Pot,R,z,use_physical=False)))
docs: NAME:
      
          flattening
      
      PURPOSE:
      
         calculate the potential flattening, defined as sqrt(fabs(z/R F_R/F_z))
      
      INPUT:
  
          Pot - Potential instance or list thereof
      
          R - Galactocentric radius (can be Quantity)
          
          z - height (can be Quantity)
      
      OUTPUT:
      
          flattening
      
      HISTORY:
      
          2012-09-13 - Written - Bovy (IAS)