Toda lattice


The Toda lattice, introduced by, is a simple model for a one-dimensional crystal
in solid state physics. It is given by a chain of particles with nearest neighbor interaction
described the Hamiltonian
and the equations of motion
where is the displacement of the -th particle from its equilibrium position,
and is its momentum,
and the Toda potential.

Soliton solutions

solutions are solitary waves spreading in time with no change to their shape and size and interacting with each other in a particle-like way. The general N-soliton solution of the equation is
where
with
where
and

Integrability

The Toda lattice is a prototypical example of a completely integrable system. To see this one uses Flaschka's variables
such that the Toda lattice reads
To show that the system is completely integrable, it suffices to find a Lax pair, that is, two operators L and P in the Hilbert space of square summable sequences such that the Lax equation
is equivalent to the time derivative of Flaschka's variables. The choice
where f and f are the shift operators, implies that the operators L for different t are unitarily equivalent.
The matrix has the property that its eigenvalues are invariant in time. These eigenvalues constitute independent integrals of motion, therefore the Toda lattice is completely integrable.
In particular, the Toda lattice can be solved by virtue of the inverse scattering transform for the Jacobi operator L. The main result implies that arbitrary decaying initial conditions asymptotically for large t split into a sum of solitons and a decaying dispersive part.