def reduced_mass(a,b):
    """
    Calculates the reduced mass for mass a and mass b

    Parameters
    ----------
    a : Float
        Mass value.
    b : Float
        Mass value.

    Returns
    -------
    red_m : Float
        Reduced mass of masses a and b. 

    """
    red_m = (a*b)/(a+b)
    return red_m