Matlab and SimMechanics Ode functions

Hello,

I use both Matlab and SimMechanics to do simulations and compare if they are the same. I noticed that the ode solver for Matlab and SimMechanics are not exactly the same, which causes some differences on the results. Now, I use ode45 for Matlab and ode3 for SimMechanics. Does anyone one know the equivalent solver for ode45 or ode3, or the ode solvers that are equivalent both in Matlab and SimMechanics?

thanks,

Saxon

Answer 1

[Walter Roberson]

When you use different solvers, even if in theory they converge to the same point, in practice the different algorithmic flows, different step sizes, and so on, will result in differences in round-off. If your system is unstable those differences in round-off can get magnified greatly (I think one of the Simulink examples specifically shows an unstable system for illustration.)

Even if the system is stable, if the algorithms are not coded exactly the same way, you will get round-off error. This is inescapable in any finite mathematical system, no matter what precision you use.