def angle(v1, v2):
    """find the angle between two 3D vectors.

    Parameters
    ----------
    v1 : list, first vector
    v2 : list, second vector

    Returns
    -------
    angle : float, the angle
    """
    return np.arccos(np.dot(v1, v2) /
                     (np.linalg.norm(v1) * np.linalg.norm(v2)))
find the angle between two 3D vectors.

    Parameters
    ----------
    v1 : list, first vector
    v2 : list, second vector

    Returns
    -------
    angle : float, the angle
    
pyod/models/rod.py