Hi @arya, those are all good questions. I haven’t actually tried to use the built in Stan ODE integrator functions. For accuracy comparisons I was comparing against an RK4 integrator with a fixed time step that I coded myself. I suppose it would be worth comparing at some point. However, the models I am working with are forced by multiple daily weather variables and I couldn’t figure out a convenient way to get the data in and aligned with the right time point within the Stan rk45 integrator.
I know there are some others who have experimented with Euler integration (e.g. Costs/benefits of solving large ODE systems as systems of difference equations/in discrete time). You may want to post your question as its own topic. You might get a better response.