On the cardinality of solutions of multilinear differential equations and applications.
As a numerical method for solving ordinary differential equations , the improved Euler method is not assumed to give exact solutions. In this paper we classify all cases where this method gives the exact solution for all initial conditions. We reduce an infinite system of partial differential equations for to a finite system that is sufficient and necessary for the improved Euler method to give the exact solution. The improved Euler method is the simplest explicit second order Runge-Kutta method....
Nous considérons un germe de 1-forme analytique dans dont le 1-jet est . Nous montrons que si l’équation définit un centre (i.e toutes les courbes solutions sont des cycles) il existe une involution analytique de préservant le portrait de phase du système. Géométriquement ceci signifie que les centres analytiques nilpotents sont obtenus par image réciproque par des applications pli. Un théorème de conjugaison équivariante permet d’obtenir une classification complète de ces centres.
The generalized linear differential equation where and the matrices are regular, can be transformed using the notion of a logarithimc prolongation along an increasing function. This method enables to derive various results about generalized LDE from the well-known properties of ordinary LDE. As an example, the variational stability of the generalized LDE is investigated.
The canonical form theorem, applied to a certain group of symmetry transformations of certain Fuchsian equations, leads automatically to the integration of them. The result can be extended to any n-order differential equation possesing a certain pointlike group of symmetries with a maximal abelian Lie-subgroup of order c.