# Problem understanding results of DiffEqUncertainty

**URL:** <https://discourse.julialang.org/t/problem-understanding-results-of-diffequncertainty/71193>\
**Category:** Modelling & Simulations\
**Tags:** question, diffeq\
**Created:** [November 9, 2021, 9:22am UTC](https://discourse.julialang.org/t/problem-understanding-results-of-diffequncertainty/71193 "2021-11-09T09:22:40Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [November 10, 2021, 11:12am UTC](https://discourse.julialang.org/t/problem-understanding-results-of-diffequncertainty/71193/4 "2021-11-10T11:12:58Z")

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> [@MrBellamy](#):
>
> What I found in the doc about Rodas5 is that : “Currently has a Hermite interpolant because its stiff-aware 3rd order interpolant is not yet implemented”. Is this the reason why I should not use it ?

It’s much more explicit than that in the docs.

[https://diffeq.sciml.ai/stable/solvers/dae\_solve/#Rosenbrock-Methods](https://diffeq.sciml.ai/stable/solvers/dae_solve/#Rosenbrock-Methods)

> - `Rodas5` - A 5th order A-stable stiffly stable Rosenbrock method. Currently has a Hermite interpolant because its stiff-aware 3rd order interpolant is not yet implemented. This means the interpolation is inaccurate on algebraic variables, meaning this algorithm should not be used with `saveat` or post-solution interpolation on DAEs.

So if the non-smooth behavior was in the algebraic variables, then that would be the explanation. If it’s in the differential variables, and that explosion… I think you might be doing something wrong in your `f` function. See:

> [@PSA: How to help yourself debug differential equation solving issues](https://discourse.julialang.org/t/psa-how-to-help-yourself-debug-differential-equation-solving-issues/62489):
>
> Debugging differential equation solver issues almost always boils down to doing the same thing, so this is a summary to help you out. For more information on specific issues, check out the FAQ section of the DifferentialEquations.jl documentation which highlights common issues and questions: [https://diffeq.sciml.ai/dev/basics/faq/](https://diffeq.sciml.ai/dev/basics/faq/)How do I debug why the differential equation solver is diverging? dt \<= dtmin. Aborting. There is either an error in your model specification or the true solution i…

One guess, do you happen to modify `u`?

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