A new use of nonlocal symmetries for computing Liouvillian first integrals of rational second order ordinary differential equations

TL;DR

This paper introduces an efficient algorithmic method leveraging nonlocal symmetries to compute Liouvillian first integrals of rational second order ODEs, improving the process of finding integrating factors.

Contribution

The paper develops a new algorithm to find nonlocal symmetries of rational 2ODEs and uses these symmetries to construct polynomial vector fields for easier integration.

Findings

The method efficiently computes nonlocal symmetries algorithmically.

It enables construction of polynomial vector fields sharing the Liouvillian first integral.

The approach simplifies the process of finding integrating factors for rational 2ODEs.

Abstract

Here we present an efficient method for finding and using a nonlocal symmetry admitted by a rational second order ordinary differential equation (rational 2ODE) in order to find a Liouvillian first integral (belonging to a vast class of Liouvillian functions). In a first stage, we construct an algorithm (improving the methodde veloped in [1]) that computes a nonlocal symmetry of a rational 2ODE. In ase cond stage, based on the knowledge of this symmetry, it is possible to construct three polynomial vector fields (in R2), which "share" the Liouvillian first integral with the rational 2ODE. These "plane" polynomial vector fields can be used to construct a procedure (based on an idea developed in [2]) to determine an integrating factor for the rational 2ODE with a fast probabilistic algorithm. The main advantages of the proposed method are: the obtaining of the nonlocal symmetry is algorithmic and very efficient and, furthermore, its use to find an integrating factor is a sequence of linear or quasilinear processes.