# Precision issues in exponent computation and differential equation

**URL:** https://discourse.julialang.org/t/precision-issues-in-exponent-computation-and-differential-equation/129591
**Category:** New to Julia
**Tags:** question, differentialequation
**Created:** [June 3, 2025, 8:59am UTC](https://discourse.julialang.org/t/precision-issues-in-exponent-computation-and-differential-equation/129591 "2025-06-03T08:59:03Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![Sahil\_Khan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sahil_khan/32/47573_2.png) [@Sahil\_Khan](https://discourse.julialang.org/u/Sahil_Khan)
#### Post date: [June 3, 2025, 8:59am UTC](https://discourse.julialang.org/t/precision-issues-in-exponent-computation-and-differential-equation/129591/1 "2025-06-03T08:59:03Z")

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Hello,

Im working on a differential equation based model some of its equations has power term (x^a) which is major issue because without this model works fine. Now issue is that I have used `stiff solver(RodasP5), different tolerence levels (1e-2 - 1e-15), maxiters, passing dt` but still its of no help.

I see NaN issues, negative values although system should be always positive. So, I also used callbacks which helps with positivity but still system is very unstable and just produces NaN. Solver fails even at t = 0.0.

Can you guys suggest something or point me to any related discussion if you know about. 🙂

Thank you

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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: [June 3, 2025, 9:04am UTC](https://discourse.julialang.org/t/precision-issues-in-exponent-computation-and-differential-equation/129591/2 "2025-06-03T09:04:14Z")

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Share some equations.

> [@Sahil\_Khan](#):
>
> I see NaN issues, negative values although system should be always positive.

How did you prove that?

> [@Sahil\_Khan](#):
>
> Solver fails even at t = 0.0.

What value is NaN in the derivative at t=0?

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### Author: ![Sahil\_Khan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sahil_khan/32/47573_2.png) [@Sahil\_Khan](https://discourse.julialang.org/u/Sahil_Khan)
#### Post date: [June 3, 2025, 9:30am UTC](https://discourse.julialang.org/t/precision-issues-in-exponent-computation-and-differential-equation/129591/3 "2025-06-03T09:30:25Z")

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Im making a small working model where I could mimic these issue. I cant share actual model unfortunately 🥲 . I will post here with result.