Electronic Journal of Differential Equations,
Vol. 2010(2010), No. 40, pp. 1-24.

Title: Time averaging for ordinary differential equations and retarded
       functional differential equations
       
Authors: Mustapha Lakrib (Univ. Djillali Liabes, Algerie)
         Tewfik Sari  (Univ. de Haute Alsace, France)

Abstract:
 We prove averaging theorems for non-autonomous ordinary
 differential equations and retarded functional differential equations
 in the case where the vector fields are continuous in the spatial
 variable uniformly with respect to the time and the solution of
 the averaged system exists on some given interval.
 Our assumptions are weaker than those required in the results of
 the existing literature. Usually, we require that the non-autonomous
 differential equation and the autonomous averaged equation
 are locally Lipschitz and that the solutions of both equations
 exist on some given interval. Our results are formulated in classical
 mathematics. Their proofs use the stroboscopic method which is
 a tool of the nonstandard asymptotic theory of differential equations.
	 
Submitted September 15, 2009. Published March 19, 2010.
Math Subject Classifications: 34C29, 34C15, 34K25, 34E10, 34E18.
Key Words: Averaging; ordinary differential equations; stroboscopic method;
  retarded functional differential equations; nonstandard analysis.