# Cvodes error

**URL:** <https://discourse.julialang.org/t/cvodes-error/78175>\
**Category:** Modelling & Simulations\
**Tags:** diffeq\
**Created:** [March 20, 2022, 7:52pm UTC](https://discourse.julialang.org/t/cvodes-error/78175 "2022-03-20T19:52:30Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Yinmin\_Liu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yinmin_liu/32/31880_2.png) [@Yinmin\_Liu](https://discourse.julialang.org/u/Yinmin_Liu)\
**Post date:** [March 20, 2022, 7:52pm UTC](https://discourse.julialang.org/t/cvodes-error/78175/1 "2022-03-20T19:52:30Z")

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Hi,

I am trying to solve a very large stiff system with the CVODE\_BDF() solver. When I apply the Jacobian-free solver by setting linear\_solver =: GMRES, it magically solved my problem with about 20 sec, which I believe is too good to be real.

Upon checking the output, I noticed that the results do not satisfy physical understanding. In some smaller system, I can get reasonable output by decreasing the relative tolerance. But in the big system I really want to solve, when I decreasing reltol, I always get the error info below:

 ![image](https://global.discourse-cdn.com/julialang/original/3X/a/5/a585cf7f771cbb5406cead9e8e67c7cf7e2594fb.png)

It seems adjusting dtmin and dtmax do not make any difference. I wonder what are the possible workarounds to this error information?

Thanks in advance!

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<div class="post-metadata">

**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:** [March 21, 2022, 12:28am UTC](https://discourse.julialang.org/t/cvodes-error/78175/2 "2022-03-21T00:28:31Z")

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> [@Yinmin\_Liu](#):
>
> It seems adjusting dtmin and dtmax do not make any difference. I wonder what are the possible workarounds to this error information?

That means the solver went unstable. 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)