Examples for `CVodeResizeHistory` when `y` changes size

CVodeResizeHistory is a very nice function and I am glad it was released in v7.3.0. I'm working on a project that requires dynamically resizing the ODE system during integration using CVodeResizeHistory(). While the documentation explains the API, I’m unclear on how to handle some scenarios.

1. Resizing when the solution vector y changes size

• When the ODE system increases or decreases in size, how should y_hist and f_hist be constructed to accommodate the new variables?

• For example, consider this case:

  Time	t_n	t_{n-1}	t_{n-2}	t_{n-3}
  Number of equations	6	5	4	5
  Notes	y6 added	shrinks below original	intermediate (y1) or last (y5) removed	back to original size

• What should the sizes of y_hist and f_hist be in this case?
  At t_n, should the sizes of the vectors in history remain as [6, 5, 4, 5], or should all history vectors be resized to [6, 6, 6, 6] to match the new system size?

• If resizing history vectors, how should the new components be filled? Is zero-initialization acceptable, or should they be extrapolated or estimated in a specific way?

2. Clarification on test behavior

In this test case, I noticed two different behaviors:
https://github.com/LLNL/sundials/blob/967f4d9d18563b8d0f7c79d056a7d1fa607f145a/test/unit_tests/cvode/CXX_serial/cv_test_resize_history.cpp#L127-L129

• Resizing while keeping the same problem size
• Growing the problem by one element each time step

Could you clarify the purpose of each approach? How do they differ in terms of results, stability, or accuracy?

3. Request for a complete working example

It would be incredibly helpful to see a full example that demonstrates a dynamic resize where the number of unknowns (NEQ) both expands and shrinks

Thank you for your work on this excellent integration library!