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arXiv 2304.10697nlin.SImath.COmath.DS
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对称Toda、梯度流与三对角化

Symmetric Toda, gradient flows, and tridiagonalization

Anthony M. Bloch, Steven N. Karp

AI总结:

本文利用对称Toda流微分同胚于旗流形上扭曲梯度流的事实,自然推导了其三对角化过程,将其分解并映射回三对角Toda晶格流,并借助完全正性理论研究了投影到permutohedron乘积上的流。

摘要:

Toda晶格(1967)是一个由直线上受指数势支配的n个点给出的哈密顿系统。Flaschka(1974)通过将其解释为对称三对角n×n矩阵空间上的流,证明了Toda晶格是可积的,而Moser(1975)证明了它是射影空间上的梯度流。Deift、Li、Nanda和Tomei(1986)的对称Toda流将Toda晶格流从三对角矩阵推广到所有对称矩阵。他们证明了该流是可积的,即在其2d维相空间上具有d个对合积分的经典意义下。该系统也可以用其他方式视为可积。首先,Symes(1980, 1982)通过QR分解和共轭显式地求解了它。其次,Deift、Li、Nanda和Tomei(1986)将该系统“三对角化”为一族可解且可积的三对角Toda晶格。在本文中,我们利用对称Toda流微分同胚于旗流形上的扭曲梯度流这一事实,自然地推导了他们的三对角化过程,该流随后可分解为Grassmann流形乘积上的流。这些流进而可通过Plücker嵌入嵌入到射影空间中,并使用Moser的构造映射回三对角Toda晶格流。此外,我们利用Bloch、Flaschka和Ratiu(1990)的扭曲矩量图,研究了投影到permutohedron乘积上的三对角化流。这些思想在完全正性理论的自然辅助下得以实现,并基于我们之前的工作(2023)。

英文摘要:

The Toda lattice (1967) is a Hamiltonian system given by $n$ points on a line governed by an exponential potential. Flaschka (1974) showed that the Toda lattice is integrable by interpreting it as a flow on the space of symmetric tridiagonal $n\times n$ matrices, while Moser (1975) showed that it is a gradient flow on a projective space. The symmetric Toda flow of Deift, Li, Nanda, and Tomei (1986) generalizes the Toda lattice flow from tridiagonal to all symmetric matrices. They showed the flow is integrable, in the classical sense of having $d$ integrals in involution on its $2d$-dimensional phase space. The system may be viewed as integrable in other ways as well. Firstly, Symes (1980, 1982) solved it explicitly via $QR$-factorization and conjugation. Secondly, Deift, Li, Nanda, and Tomei (1986) 'tridiagonalized' the system into a family of tridiagonal Toda lattices which are solvable and integrable. In this paper we derive their tridiagonalization procedure in a natural way using the fact that the symmetric Toda flow is diffeomorphic to a twisted gradient flow on a flag variety, which may then be decomposed into flows on a product of Grassmannians. These flows may in turn be embedded into projective spaces via Plücker embeddings, and mapped back to tridiagonal Toda lattice flows using Moser's construction. In addition, we study the tridiagonalized flows projected onto a product of permutohedra, using the twisted moment map of Bloch, Flaschka, and Ratiu (1990). These ideas are facilitated in a natural way by the theory of total positivity, building on our previous work (2023).

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