Elastic and inelastic line-soliton solutions of the   Kadomtsev-Petviashvili II equation
  The Kadomtsev-Petviashvili II (KPII) equation admits a large variety of multi-soliton solutions which exhibit both elastic as well as inelastic types of interactions. This work investigates a general class of multi-solitons which were not previously studied, and which do not in general conserve the number of line solitons after interaction. The incoming and outgoing line solitons for these solutions are explicitly characterized by analyzing the $\tau$-function generating such solutions. A special family of $N$-soliton solutions is also considered in this article. These solutions are characterized by elastic soliton interactions, in the sense that amplitude and directions of the individual line solitons as $y\to\infty$ are the same as those of the individual line solitons as $y\to-\infty$. It is shown that the solution space of these elastic $N$-soliton solutions can be classified into $(2N-1)!!$ disjoint sectors which are characterized in terms of the amplitudes and directions of the $N$ line solitons. 
Gino Biondini and Sarbarish Chakravarty