def lu_chen(XYZ, t, a=-10, b=-4, c=18.1):
    """
    The Lu-Chen Attractor.
    x0 = (0.1,0.1,0.1)
    """
    x, y, z = XYZ
    x_dt = -a * b / (a + b) * x - y * z + c
    y_dt = a * y + x * z
    z_dt = b * z + x * y
    return x_dt, y_dt, z_dt