def efficency_poly(cappa):
    """Calculate efficency for a given pump's typical number.

    The polynomial has been calculated applaying the curve fitting at nodes
    cappa       .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.1 1.2
    eta         .700 .850 .900 .916 .923 .928 .931 .932 .933 .935 .932
    weights     ones(cappa)
    n           5

    :param cappa (float): typical number
    :return eta (float): efficency
    """
    coef = [-0.171, 7.400, -19.717, 25.671, -16.239, 3.990]
    eta = sum([val * cappa**idx for idx, val in enumerate(coef)])

    return eta