def add(v,w):
    """Add two vectors.

    Parameters
    ----------
    v : list
        A 3D vector.
    w : list
        A 3D vector.

    Returns
    -------
    tuple
        Returns the `v` + `w`.

    Examples
    --------
    >>> from .pycgmKinetics import add
    >>> v = [1, 2, 3]
    >>> w = [4, 5, 6]
    >>> add(v, w)
    (5, 7, 9)
    """
    x,y,z = v
    X,Y,Z = w
    return (x+X, y+Y, z+Z)