variation of constant (in ODE)

*To*: mathgroup at smc.vnet.net*Subject*: [mg14489] variation of constant (in ODE)*From*: "Alexander D. Khilinsky" <smiles at chat.ru>*Date*: Fri, 23 Oct 1998 20:59:09 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Hi ! Does anybody know, where I can find the Mathematica package,which implement the method "variation of constant" (uses in solving ODE). Particularly, I need the implementation of methods of perturbation theory, for example,method of Bogolubov-Krylov-Mitropolsky. For example, I have equation : u''(x) + u(x) + eps*u(x)^2 == 0 and I know that u(x) = a*cos(t+b), where a=a(t),b=b(t). I want to know the OD equations for a(t), and b(t).