def visc_rad_kap_sc(T,rho,X):
    '''
    Radiative viscosity (Thomas, 1930) for e- scattering opacity

    Parameters
    ----------
    X : float
       H mass fraction
    T : float
       temperature in K
    rho : float
       density in cgs

    Returns
    -------
    nu : float
       radiative diffusivity in [cm**2/s]

    Examples
    --------
    >>> In [1]: import astronomy as ast
    >>> In [2]: l = 100*1.e5 # 100km
    >>> In [3]: v = 1.e5     # typical velocity
    >>> In [4]: T   = 90.e6  # temperature
    >>> In [5]: X   = 0.001  # H mass fraction
    >>> In [6]: rho = 100.   # density
    >>> In [7]: nu = ast.visc_rad_kap_sc(T,rho,X)
    >>> In [8]: Re=v*l/nu
    >>> In [9]: print "Re_rad = "+str('%g'%Re)
    >>> Re_rad = 4.43512e+08

    Notes
    -----
    Eqn. 14' in Schatzman, 1977, assume electron scattering opacity
    kappa_sc = 0.2*(1+X), Kippenhahn (2nd edn, Eqn 17.2)

    '''
    kappa = 0.2*(1.+X)
    nu_rad = 6.88e-26*(old_div(T**4,(kappa*rho**2)))
    return nu_rad
def visc_rad_kap_sc ( T , rho , X ) : kappa = 0.2 * ( 1. + X ) nu_rad = 6.88e-26 * ( old_div ( T ** 4 , ( kappa * rho ** 2 ) ) ) return nu_rad
Radiative viscosity (Thomas, 1930) for e- scattering opacity

    Parameters
    ----------
    X : float
       H mass fraction
    T : float
       temperature in K
    rho : float
       density in cgs

    Returns
    -------
    nu : float
       radiative diffusivity in [cm**2/s]

    Examples
    --------
    >>> In [1]: import astronomy as ast
    >>> In [2]: l = 100*1.e5 # 100km
    >>> In [3]: v = 1.e5     # typical velocity
    >>> In [4]: T   = 90.e6  # temperature
    >>> In [5]: X   = 0.001  # H mass fraction
    >>> In [6]: rho = 100.   # density
    >>> In [7]: nu = ast.visc_rad_kap_sc(T,rho,X)
    >>> In [8]: Re=v*l/nu
    >>> In [9]: print "Re_rad = "+str('%g'%Re)
    >>> Re_rad = 4.43512e+08

    Notes
    -----
    Eqn. 14' in Schatzman, 1977, assume electron scattering opacity
    kappa_sc = 0.2*(1+X), Kippenhahn (2nd edn, Eqn 17.2)