def converge(lhs, rhs):
    """
    Determine convergence factor.

    :param lhs: (flt)
    :param rhs: (flt)
    :param div: (flt)
    :return: multiplication factor (flt) ((lhs / rhs) - 1) / div + 1
    """
    lhs = abs(lhs)
    rhs = abs(rhs)
    div = max(lhs, rhs) / min(lhs, rhs) * 2
    return (rhs / lhs - 1) / div + 1
