Exact solutions to the modified Korteweg-de Vries equation

Abstract

A formula for certain exact solutions to the modified Korteweg-de Vries (mKdV) equation is obtained via the inverse scattering transform method. The kernel of the relevant Marchenko integral equation is written with the help of matrix exponentials as $$\Omega (x+y;t)=C{e}^{-(x+y)A}{e}^{8A^{3}t}B,$$ where the real matrix triplet $(A,B,C)$ consists of a constant $p\times p$ matrix $A$ with eigenvalues having positive real parts, a constant $p\times 1$ matrix $B$, and a constant $1\times p$ matrix $C$ for a positive integer $p$. Using separation of variables, the Marchenko integral equation is explicitly solved yielding exact solutions to the mKdV equation. These solutions are constructed in terms of the unique solution $P$ to the Sylvester equation $AP+PA=BC$ or in terms of the unique solutions $Q$ and $N$ to the respective Lyapunov equations $A^{†}Q+QA=C^{†}C$ and $AN+N{A}^{†}=B{B}^{†}$, where the $†$ denotes the matrix conjugate transpose. Two interesting examples are provided.

15 pages, 1 figure