def FES(x):
    """
    This function calculates the value(s) of free energy given the value(s) of CV.

    Parameters
    ----------

    x : float or np.array
        value of CV

    Returns
    -------

    y : float or np.array
        value of free energy

    Examples
    --------

    >>> FES(1.822)
    2.390088592634875

    >>> FES(np.arange(0,10,1))    print(x)
    array([6.84595   , 2.55345581, 2.63137371, 4.87913363, 7.07697797,
           7.7159    , 6.38054805, 3.78509539, 1.46207595, 1.10418573])
    """

    coef = [-0.000481992, 0.0133127, -0.102597,
            -0.0406179, 2.84049, -7.0026, 6.84595]
    y = 0
    for i in range(len(coef)):
        y += coef[i] * x ** (6 - i)
    return y