def vector_from_points(a, b):
    """Construct a vector from two points.

    Parameters
    ----------
    a : sequence of float
        XYZ coordinates of first point.
    b : sequence of float
        XYZ coordinates of second point.

    Returns
    -------
    ab : sequence of float
        The vector from ``a`` to ``b``.

    Examples
    --------
    >>>

    """
    return b[0] - a[0], b[1] - a[1], b[2] - a[2]
