# Error thrown when attempting Parameter Identifiability

**URL:** <https://discourse.julialang.org/t/error-thrown-when-attempting-parameter-identifiability/102440>\
**Category:** General Usage\
**Tags:** package, diffeq, sciml, modelingtoolkit, parameters\
**Created:** [August 3, 2023, 10:52am UTC](https://discourse.julialang.org/t/error-thrown-when-attempting-parameter-identifiability/102440 "2023-08-03T10:52:33Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![CurioMath](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/curiomath/32/43603_2.png) [@CurioMath](https://discourse.julialang.org/u/CurioMath)\
**Post date:** [August 3, 2023, 10:52am UTC](https://discourse.julialang.org/t/error-thrown-when-attempting-parameter-identifiability/102440/1 "2023-08-03T10:52:33Z")

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Hi,

I’m really excited to dig around the Parameter Identifiability in ODE Models, that I came across in ModelingToolkit.jl as well as in Overview of Julia’s SciML documentation. I have tried the same on my ODE model, but face some bottlenecks with certain equations involving exponents.

The error thrown is :  
MethodError: no method matching ^(::Nemo.QQMPolyRingElem, ::Rational{Int64})

I have troubleshooted my code and found that the below equation with decimal exponent is the root cause of error:

```julia
x1 ~ 423.1*(x2^0.2561)

```

But I’m left with no choice to alter my equation, since it is fitted out of data. Can’t such type of equations be handled in parameter identifiability? I could simulate the model, solving my system of equations with the above mentioned equation as well…and this issue arises only when I go for parameter identifiability.

Can I know why this occurs and how can it be resolved?  
Thanks in advance!

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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:** [August 3, 2023, 1:11pm UTC](https://discourse.julialang.org/t/error-thrown-when-attempting-parameter-identifiability/102440/2 "2023-08-03T13:11:26Z")

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> [@CurioMath](#):
>
> Can’t such type of equations be handled in parameter identifiability?

No, it can only do rational polynomial equations.

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<div class="post-metadata">

**Author:** ![CurioMath](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/curiomath/32/43603_2.png) [@CurioMath](https://discourse.julialang.org/u/CurioMath)\
**Post date:** [August 4, 2023, 5:29am UTC](https://discourse.julialang.org/t/error-thrown-when-attempting-parameter-identifiability/102440/3 "2023-08-04T05:29:06Z")

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Thanks for the info!