Save a simplified ModelingToolkit problem as text

Specific Domains Modelling & Simulations
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Because structural_simplify is slow, I want to write the simplified system to a file, from where I can load it later. Using serialize("sys.bin", sys) works, but this causes problems when switching between julia versions, and with undefined variables when creating getter functions… Is there a way to write and load the simplified system as text in a human-readable format?

I guess it should be possible to write unknowns(sys), equations(sys) etc... to a file in the correct format, so that you can create a model from it again. Maybe someone has done this before?

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I got problems and systems mixed up here. I think that serializing the ODESystem and not the ODEProblem will solve the errors I am getting with the getu and setu functions. But it is not clear to me how I can serialize just the ODESystem and the initialization system: how can I pass a deserialized initialization system to the ODEProblem constructor?

What I am trying to achieve:

sys = ODESystem(eqs, t)
isys = generate_initializesystem(sys)
serialize("test.bin", (sys, isys))
sys, isys = deserialize("test.bin")
prob = ODEProblem(sys, u0map, tspan; isys)

@ChrisRackauckas

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Does ODEProblemExpr do what you want?

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How can I convert an ODEProblemExpr back into an ODEProblem ?

UPDATE:
The following approach works:

expr = ODEProblemExpr(s.sys, defaults, (0.0, dt); guesses)
prob = eval(expr)

But now solving the problem is 100 times slower than before. Perhpas ODEProblemExpr does not store the simplified problem, but the original problem?

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It should be the simplified problem? It is effectively what is stated in the OP, i.e. using equations(sys), etc. and then writing a Julia expression that would be the expression to reconstruct itself. If you run that after simplification, then equations(sys) etc. are the changed versions and so it should “just work” (and I think we test that?).

You can print it out to a file and see what the resulting system is and it should look like the . If it’s giving something incorrect, please open an issue.

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Note that since it’s just a Julia file, if you put it into a repo and call it then it will play nicely with package precompilation and store the binary.

1 Like
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I found this old issue: Save expressions to .jl? · Issue #253 · JuliaIO/FileIO.jl · GitHub. I guess this is the missing link for actually writing this expression to a .jl file…