Quasi-line soliton interactions of the Davey–Stewartson I equation: on the existence of long-range interaction between two quasi-line solitons through a periodic soliton

A periodic soliton is turned into a line soliton accordingly as a parameter point approaches to the boundary of the existing domain in the parameter space for a nonsingular periodic-soliton solution. We will call the periodic soliton with parameters of the neighborhood of the boundary a quasi-line soliton in this paper, which seems to be the line soliton. The interaction between two quasi-line solitons is the same as the interaction between two line solitons, except for very small parameter-sensitive regions. However, in such parameter regions, there are new long-range interactions between two quasi-line solitons through the periodic soliton as the messenger under some conditions, which cannot be described by the two-line-soliton solution.