General N-solitons and their dynamics in several nonlocal nonlinear Schrödinger equations

General N-solitons in three recently-proposed nonlocal nonlinear Schrödinger equations are presented. These nonlocal equations include the reverse-space, reverse-time, and reverse-space–time nonlinear Schrödinger equations, which are nonlocal reductions of the Ablowitz–Kaup–Newell–Segur (AKNS) hierarchy. It is shown that general N-solitons in these different equations can be derived from the same Riemann–Hilbert solutions of the AKNS hierarchy, except that symmetry relations on the scattering data are different for these equations. This Riemann–Hilbert framework allows us to identify new types of solitons with novel eigenvalue configurations in the spectral plane. Dynamics of N-solitons in these equations is also explored. In all the three nonlocal equations, their solutions often collapse repeatedly, but can remain bounded or nonsingular for wide ranges of soliton parameters as well. In addition, it is found that multi-solitons can behave very differently from fundamental solitons and may not correspond to a nonlinear superposition of fundamental solitons.     

Error propagation when approximating multi-solitons: The KdV equation as a case study

The paper studies the influence of the time discretizations when simulating some phenomena involving more than one solitary wave. Taking the KdV equation as a case study, we obtain some conditions on the numerical method in order to get a more correct simulation of multi-soliton solutions. They are related to the evolution of the conserved quantities of the problem through the numerical integration. It is shown that, when approximating N-solitons, a method that preserves N invariants of the problem shows a better time propagation of the error than that of a general scheme. As a consequence of this, the simulation of some physical parameters that characterize the waves is more suitable when using conservative integrators. We also show how these results can be extended to the approximation to multi-solitons of any equation of the KdV hierarchy and, more generally, other integrable equations.     

Non dispersive solutions of the generalized Korteweg-de Vries equations are typically multi-solitons

We consider solutions of the generalized Korteweg-de Vries equations (gKdV) which are non dispersive in some sense and which remain close to multi-solitons. We show that these solutions are necessarily pure multi-solitons. For the Korteweg-de Vries equation (KdV) and the modified Korteweg-de Vries equation (mKdV) in particular, we obtain a characterization of multi-solitons and multi-breathers in terms of non dispersion.