Evaluating the rhs of ODE

New to Julia
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1

Hi!

I am a beginner with Julia, just a week since I started learning Julia. I am having an issue with evaluating the rhs of a big ODE with 46 variables and more than a hundred parameters. The ODE was originally written in Mathematica and I translated it in Python, I am ending up having a numerical issue with the integration. So to debug the code I want to compare rhs of Python vs Julia. Indeed the Mathematica version was quickly translated in Julia and the integration works just fine.

Here is the link for the code

2

That all sounds pretty good up to this point, what’s the issue?

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The issue is that I don’t know how to pass the vector of the variables to the rhs of the ODE to evaluate it.

4

Isn’t it possible to come up with some (really) minimal working example (MWE)? Perhaps it is possible to describe your problem with something as simple as a solution to the “hello-world” differential equation \dot x(t) = -5x(t).

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Here is the code Chilperic Armel Foko / Model Julia · GitLab

6

Whatever is flagging your posts is a false positive. I’ll say sorry for the community and the mods should help this out.

It looks like you’re using ModelingToolkit.jl. What you’re looking for is:

https://mtk.sciml.ai/dev/systems/ODESystem/#SciMLBase.ODEFunction

It’ll create the standard DifferentialEquations.jl functions f(u,p,t) and f(du,u,p,t) where u follows the variable order of states(sys) and p follows the order of parameters(sys) (and as it shows, you can override the order if you please). Hopefully that helps.

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Exactly it was I am using. The constructor does not allow me to evaluate the rhs

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If you use ODEFunction(sys) you’ll get the function.

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