# Nonlinear systems and ModelingToolkitStandardLibrary

**URL:** https://discourse.julialang.org/t/nonlinear-systems-and-modelingtoolkitstandardlibrary/99460
**Category:** Modelling & Simulations
**Created:** [May 26, 2023, 8:11pm UTC](https://discourse.julialang.org/t/nonlinear-systems-and-modelingtoolkitstandardlibrary/99460 "2023-05-26T20:11:52Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Paulo\_Jabardo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/paulo_jabardo/32/3196_2.png) [@Paulo\_Jabardo](https://discourse.julialang.org/u/Paulo_Jabardo)
#### Post date: [May 26, 2023, 8:11pm UTC](https://discourse.julialang.org/t/nonlinear-systems-and-modelingtoolkitstandardlibrary/99460/1 "2023-05-26T20:11:52Z")

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Much work in thermal/fluid problems involve steady state cases. I have been playing around with NonlinearSolve.jl and it works well. What I’m having trouble is in the integration it with ModelingToolkitStandardLibrary.jl.

I have not been able to use `NonlinearSystem` instead of `ODESystem` and I don’t know if this is even possible since the components in ModelingToolkitStandardLibrary.jl extend `ODESystem`.

If every component has has zero time derivatives, `ODESystem` and `structural_simplify` return a nonlinear system of equations as expected (it is a DAE solver after all…) that can be integrated using something like

```julia-repl
sys = structural_simplify(model)
prob = ODAEProblem(sys, Pair[], (0, 10.0))
sol = solve(prob, Tsit5())

```

and the solution will have two time steps: the first and the last (as expected). Is it possible to use `NonlinearSystem` directly or is this ‘hack’ is the only/best approach?

Thanks  
Paulo

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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: [May 26, 2023, 8:31pm UTC](https://discourse.julialang.org/t/nonlinear-systems-and-modelingtoolkitstandardlibrary/99460/2 "2023-05-26T20:31:48Z")

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> [@Paulo\_Jabardo](#):
>
> I have not been able to use `NonlinearSystem` instead of `ODESystem` and I don’t know if this is even possible since the components in ModelingToolkitStandardLibrary.jl extend `ODESystem`.

You can just convert any ODESystem to a NonlinearProblem.