图4. 二孤子解, 参数为 $\delta=1,\gamma_1=\gamma_3=-1,\gamma_2=\gamma_4=1,\lambda_1=\lambda_2^*=-\frac{1}{5}-\frac{i}{5},\lambda_3=\lambda_4^*=\frac{2}{5}+\frac{2i}{5}.$
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