def init_m(pos):
    """
    This function initialises an approximate domain wall in the z direction.
    """
    z = pos[2]

    if z < 1200:
        return (0, 0, 1)
    elif 1200 <= z < 1400:
        return (1, 1, 0)
    else:
        return (0, 0, -1)