# Variations for Some Painlev\'e Equations

## TL;DR

This paper explores the properties and solutions of Painlevé equations, linking their integrability to classical solutions and using differential Galois theory to analyze their variational equations.

## Contribution

It establishes a connection between Painlevé equations' integrability and classical solutions, and applies Morales-Ramis theory for analyzing their variational equations.

## Key findings

- Complete integrability implies all solutions are classical.
- Variational equations at algebraic solutions match normal variational equations.
- Differential Galois groups are non-commutative in tested cases.

## Abstract

This paper first discusses irreducibility of a Painlev\'e equation $P$. We explain how the Painlev\'e property is helpful for the computation of special classical and algebraic solutions. As in a paper of Morales-Ruiz we associate an autonomous Hamiltonian $\mathbb{H}$ to a Painlev\'e equation $P$. Complete integrability of $\mathbb{H}$ is shown to imply that all solutions to $P$ are classical (which includes algebraic), so in particular $P$ is solvable by ''quadratures''. Next, we show that the variational equation of $P$ at a given algebraic solution coincides with the normal variational equation of $\mathbb{H}$ at the corresponding solution. Finally, we test the Morales-Ramis theorem in all cases $P_{2}$ to $P_{5}$ where algebraic solutions are present, by showing how our results lead to a quick computation of the component of the identity of the differential Galois group for the first two variational equations. As expected there are no cases where this group is commutative.