Ks. Govinder et Pgl. Leach, THE ALGEBRAIC STRUCTURE OF THE FIRST INTEGRALS OF 3RD-ORDER LINEAR-EQUATIONS, Journal of mathematical analysis and applications, 193(1), 1995, pp. 114-133
We use the Lie theory of extended groups to analyse the first integral
s of scalar third-order linear ordinary differential equations. The an
alysis reveals three natural classes for which the equation has four,
five, or seven symmetries. We show that each class has first integrals
with a specific number of symmetries. Illustrative examples of each c
lass are given. Comparison is made with the integrals of nonlinear equ
ations. (C) 1995 Academic Press, Inc.