Within my ODE function additional quantities are calculated which I would like to save to extract them later for e.g. inspection or plotting.

There is the approach with the `SavingCallback`

; however, the `save_func(u, t, integrator)`

only has access to the states.

Another option might be to use other callbacks like `ContinousCallback`

.

My idea was to extend the differential equations with additional states and setting the corresponding differential equations to zero. It works I guess, but there might be better ways? One shortcoming is that I then have to supply initial values for the additional quantities. Any other ideas?