def structure_function_kolmogorov(separation, r0):
    """
        Compute the Kolmogorov phase structure function

        Parameters:
            separation (ndarray, float): float or array of data representing
                separations between points
            r0 (float): Fried parameter for atmosphere

        Returns:
            ndarray, float: Structure function for separation(s)
    """
    return 6.88 * (separation / r0) ** (5.0 / 3.0)
