Computable Integrability. Chapter 5: Factorization of LPDOs

TL;DR

This paper discusses the factorization of linear partial differential operators (LPDOs) using BK-factorization, providing explicit conditions for factorization and exploring invariants related to classical Laplace invariants.

Contribution

It introduces BK-factorization for LPDOs of arbitrary order and links new invariants to classical Laplace invariants, advancing the understanding of operator factorization.

Findings

BK-factorization provides explicit factorization conditions for many LPDOs.

New invariants for LPDOs are constructed and related to classical Laplace invariants.

Factorization simplifies solving certain classes of differential operators.

Abstract

Different definitions of integrability, as a rule, use linearization of initial equation and/or expansion on some basic functions which are themselves solutions of some linear differential equation. Important fact here is that linearization of some differential equation is its simplification but not solving yet. For instance, in case of linear Schroedinger equation, we are not able to find its solutions explicitly but only to name them Jost functions and to exploit their useful properties (see previous Chapters). On the other hand, well-known fact is that for LODE with constant coefficients operator itself can always be factorized into first-order factors and thus the problem is reduced to the solving of a few first-order LODEs which are solvable in quadratures. In case of differential operators with variable coefficients factorization is not always possible but for the great number of operators BK-factorization gives factorization conditions explicitly which we are going to demonstrate in this Chapter. BK factorization is used to construct set of invariants for LPDO of arbitrary order; interconnections of these new invariants with classic Laplace invariants for second order hyperbolic LPDOs are discussed.