[求助]相位与庞加莱截面
 

用MatLab计算下面的非线性方程，画出相图和庞加莱截面（ψ=2*pi/3)

θ' = η
η' = -2*β*η - ω*ω*sinθ + Fcosφ
φ' = ν

取β = 1/4, ω = 1, ν = 2/3, F = 1.025, 1.07, 1.15, 1.4, 1.5

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