ControlSystems.jl VS PowerSimulationsDynamics.jl

control system toolbox -> ControlSystems.jl

Find an open-source controls library on GitHub (this one's my favorite) and search the Issues tab for something that everyone agrees would be nice to have/fix but no one has gotten around to implementing/fixing. If it's something you feel comfortable implementing, ask the maintainers if they wouldn't mind if you submitted a pull request for the new feature/bugfix.

Sure you can keep moving goal posts. Of course it doesn't make sense to bind a C production code to a C package (SUNDIALS) through Julia. But if you're asking who is using Julia bindings to SUNDIALS as part of a real case, one case that comes to mind is the Sienna power systems dynamics stuff out of NREL (https://www.nrel.gov/analysis/sienna.html). If you look inside of the dynamics part of Sienna you can clearly see IDA being used (https://github.com/NREL-Sienna/PowerSimulationsDynamics.jl). IIRC at a recent Julia meetup in the Benelux region kite model simulations also used it for the same reasons (https://github.com/aenarete/KiteSimulators.jl) which of course is pointing to the open source code organization for Aenarete (http://aenarete.eu/).

The way to find other use cases is to look through the citations. Generally there will be a pattern to it. For cases which reduce to (mass matrix) ODEs FBDF generally (but not always) outperforms CVODE's BDF these days, so those cases have mostly converted over. This includes not just ODEs but also other DAEs which are defined through ModelingToolkit, as the index reduction process generates ODEs and generally the ODE form ends up more efficient than using the original DAE form (though not always of course). It's in the fully implicit DAE form that the documentation (as of May 1st 2023) recommends using Sundials' IDA as the most efficient method for that case (https://docs.sciml.ai/DiffEqDocs/stable/solvers/dae_solve/) (yes, the docs recommend non-Julia solvers when appropriate. There's more than a few of such recommendations in the documentation). Power systems is such a case with Index-1 DAEs written in the fully implicit form which are difficult in many instances to write in mass matrix form and not already written in ModelingToolkit, hence its use of IDA here. By the same reasoning you can also search around in the citations for other use cases of IDA.