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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_mi_vec(slab):
 """ Convenience function which returns the unit vector aligned with the miller index. """

    mvec = np.cross(slab.lattice.matrix[0], slab.lattice.matrix[1])
    return mvec / np.linalg.norm(mvec)