Symplectic integration and Interpolating function

*To*: mathgroup at smc.vnet.net*Subject*: [mg45554] Symplectic integration and Interpolating function*From*: Guibout <guibout at ifrance.com>*Date*: Tue, 13 Jan 2004 04:04:08 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hi, I am using symplectic integrators to integrate a set of ode. One advantage of these integrators is that some properties are exactly preserved at the vertices. Therefore, it may be of interest to look at the values of the functions at the vertices. My question is the following: How do I find the vertices? NDSolve returns only an interpolating functions and some symplectic integrators have variable time steps, so even if I set the starting step size, I don't have any information on the next steps. Thanks Vincent