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arXiv 1707.09536nlin.SImath-phmath.MP
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非线性波的可积性和线性稳定性

Integrability and linear stability of nonlinear waves

Antonio Degasperis, Sara Lombardo, Matteo Sommacal

摘要:

众所周知,谱方法可以非常有效地研究可积偏微分方程解的线性稳定性。我们在这里提出了一个直接建设的线性化方程的本征模,只使用其相关的拉克斯对没有参考光谱数据和边界条件。这种局部构造是在一般的$N \times N$矩阵格式下给出的,从而可以应用于包括多分量非线性Schroedinger系统和多波共振相互作用系统在内的一大类可积方程。在这个一般的方法中所涉及的分析和数值计算作为一个例子详细的$N = 3$的两个耦合的非线性薛定谔方程的散焦,聚焦和混合制度的特定系统。在振幅和波数的整个参数空间中,充分讨论了连续波解的不稳定性。通过定义和计算谱变量在复平面上的谱,本征频率被明确地表达出来。根据它们的拓扑性质,这些光谱在参数空间中的完整分类,并以图形方式显示。对于一般的耦合常数选择,连续波解是线性不稳定的。

英文摘要:

It is well known that the linear stability of solutions of partial differential equations which are integrable can be very efficiently investigated by means of spectral methods. We present here a direct construction of the eigenmodes of the linearized equation by using only their associated Lax pair with no reference to spectral data and boundary conditions. This local construction is given in the general $N \times N$ matrix scheme so as to be applicable to a large class of integrable equations, including the multicomponent nonlinear Schroedinger system and the multi-wave resonant interaction system. The analytical and numerical computations involved in this general approach are detailed as an example for $N = 3$ for the particular system of two coupled nonlinear Schroedinger equations in the defocusing, focusing and mixed regimes. The instabilities of the continuous wave solutions are fully discussed in the entire parameter space of their amplitudes and wave numbers. By defining and computing the spectrum in the complex plane of the spectral variable, the eigenfrequencies are explicitly expressed. According to their topological properties, the complete classification of these spectra in the parameter space is presented and graphically displayed. The continuous wave solutions are linearly unstable for a generic choice of the coupling constants.

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