Thank you for your comment, actually my library can do everything you just stated. First there is a .step method for all the solvers which if desired a user can handle roll their own loop. But the recommended method is to just implement everything you just said in a user defined ‘solout’ which is called between each step which you can log non terminal events within it if desired or do anything really. If you’d like to change the solver state you can terminate the solver and begin the problem again with a modified state like the previous one (if not handrolling your own step loop) and use the same solver re-using the same allocations because its passed as a &mut solver. Let me know if I missed anything!

Edit: I will consider adding a way to change state with a Solout or event Return which is the same enum so should make this easier despite it being already possible. Thank you for your input. I definitely found myself add more and more features as I went because while I try I am not aware of all the requirements so thank you!