def kolmogorov_53(k, k0=50):
    """
    Customizable Kolmogorov Energy spectrum
    Returns the value(s) of k0 * k^{-5/3}

    Parameters
    ----------
    k: array-like, wavenumber: convention is k= 1/L NOT 2pi/L
    k0: float, coefficient

    Returns
    -------
    e_k: power-law spectrum with exponent -5/3 for a given k and k0
    """
    e_k = k0 * k ** (-5. / 3)
    return e_k