code: def sigma2(self,R,romberg=False,nsigma=None,phi=0.):
          
          return self.sigma2surfacemass(R,romberg,nsigma,use_physical=False)\
              /self.surfacemass(R,romberg,nsigma,use_physical=False)
docs: NAME:
  
             sigma2
  
          PURPOSE:
  
             calculate sigma_R^2 at R by marginalizing over velocity
  
          INPUT:
  
             R - radius at which to calculate sigma_R^2 density (can be Quantity)
  
          OPTIONAL INPUT:
  
             nsigma - number of sigma to integrate the velocities over
  
          KEYWORDS:
  
             romberg - if True, use a romberg integrator (default: False)
  
          OUTPUT:
  
             sigma_R^2 at R
  
          HISTORY:
  
             2010-03-XX - Written - Bovy (NYU)