Use ODE45 with a frequency span instead of time?

I have 2 coupled differential equations. I'm trying to use ODE45, but it requires a time span (tspan).

Is there a way to use a frequency span instead, or perhaps another more suitable differential equation solver?

Answer 1

[Star Strider]

It does not require that the independent variable be time. It can be whatever your differential equation system requires. If your derivatives are with respect to frequency, use a frequency vector instead.

[Keith Grey]

Can you also solve without initial conditions?

I see conditions are set for displacement. In my case, these are really low values & unknown.

[Star Strider]

The numeric ODE solvers all require initial conditions.

If you have data and you need to estimate the initial conditions (and possibly other parameters) to fit your differential equations to the data, that is relatively straightforward to do.

If your differential equations are relatively straightforward, you can use the Symbolic Math Toolbox to get an analytic solution (providing one exists). Those initial conditions can be symbolic.