def escape_velocity(M,R):
ve = np.sqrt(<NUM_LIT>*grav_const*M*msun_g/(R*rsun_cm))<EOL>ve = ve*<NUM_LIT><EOL>return ve<EOL>
escape velocity.

Parameters
----------
M : float
    Mass in solar masses.
R : float
    Radius in solar radiu.

Returns
-------
v_escape
    in km/s.