def dot(v1, v2):
    """returns dot product between two vectors, non class member.

    Parameters
    ----------
    v1: Vector
        The first vector.
    v2: Vector
        The second vector.

    Returns
    -------
    float
        The dot product of the vectors.
    """
    return v1.x * v2.x + v1.y * v2.y + v1.z * v2.z
