Toda Lattice  

In General
* Idea: One of the main examples of integrable system.
$ Def: A lattice of points on a line (infinite or finite) with equal masses, longitudinally oscillating and subject to nearest neighbor couplings, decreasing exponentially with the separation (exponentially repulsive forces).
* Lagrangian (first-order):

L = i=1N (Pi Q·iQi Pi·) – i=1N ( Pi2 + fi exp{QiQi+1}) ,

where N is the number of masses on the line, and fi a set of real coupling constants; There is also an inequivalent Lagrangian (bi-Hamiltonian structure, > see types of symplectic structures).
* Equations of motion:

Q·i = Pi ,   Pi· = fi–1 exp{Qi–1Qi} – fi exp{QiQi+1} .

* Lax pair: The pair (Lij, Aij) satisfying dL/dt = [L, A], given by

Lij = k=1n Pk ik j,k + exp{QkQk+1} (ik j,k+1 + ik+1 j,k) ,
Aij = k=1n exp{QkQk+1}(ik j,k+1ik+1 j,k) .

* Approximation: Note that the Hénon-Heiles approximation is chaotic!

References > s.a. self-dual solutions of general relativity.
@ General: Toda PRP(74); Das & Okubo AP(89); Toda 89; in Perelomov 90; Krichever & Vaninsky ht/00-in.
@ Hamiltonian: Gekhtman LMP(98) [non-abelian]; Carlet mp/04 [2D, and R-matrices]; Tsiganov JPA(07) [bi-Hamiltonian structures].
@ Properties: Anderson JMP(96)ht/95 [open N-body, solution]; Kasman JMP(97) [orthogonal polynomials]; Nimmo & Willox PRS(97) [Darboux transformations]; Calderbank JGP(00) [geometry]; Vaninsky JGP(03)mp/02 [open, and Atiyah-Hitchin bracket]; Agrotis et al mp/05 [open, super-integrability]; Likhachev et al PLA(06) [thermodynamics].
@ Related topics: Torrence JPA(87), JPA(88) [and linear wave equations], NPPS(88) [Kac-van Moerbeke lattice]; Rosquist & Goliath GRG(98)gq/97 [Lax pair, geometrized]; Gueuvoghlanian a0901 [submanifolds, Lie algebras].
@ Quantum: Ikeda JPA(94); Matsuyama AP(92), AP(01); An LMP(09) [complete set of eigenfunctions]; > s.a. deformation quantization [Moyal].

Related Systems and Generalizations
@ Generalizations: Alber LMP(89) [relativistic]; Saveliev ht/95 [integrable]; Gervais & Saveliev NPB(95)ht [higher grading]; Adler JPA(01) [arbitrary planar graph]; Santini et al PRE(04)nl.SI [2D square lattice].
@ Nearby systems: Christiansen et al LMP(93) [integrable].


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