How do I use callback_initializealg?

[tpdsantos]

Question❓

I'm trying to model a chromatographic column, which involves a second-order PDE in space. At some points in time, I change the flowrate and concentration in the beginning of the column through discrete callbacks but I get initialization errors. I tried to use the initializealg = ShampineCollocationInit() option inside solve, but to no avail. After reading #3254 I found out about the callback_initializealg option that I wanted to try, but how and where should I use it?

Thanks

[AayushSabharwal]

callback_initializealg is a lower-level detail. In MTK, you can set it by providing the reinitializealg keyword to SymbolicContinuousCallback or SymbolicDiscreteCallback. The docstring for SymbolicContinuousCallback describes this.

[tpdsantos]

I see. And how would I add this keyword considering I introduced my callbacks inside @mtkmodel in the @discrete_events environment? or would I need to provide it separately in order to use it?

[AayushSabharwal]

Just normally:

@discrete_events begin
    ModelingToolkit.SymbolicDiscreteCallback(condition, affect; reinitializealg = ShampineCollocationInit())
end

inside the @mtkmodel macro.

[tpdsantos]

Thanks a lot, the BrownFullBasicInit() works like a charm! It helped me a lot, I didn't know you could pass a function directly in the environment.

[AayushSabharwal]

I didn't know you could pass a function directly in the environment.

Yeah we aren't fully transparent about the things you can do inside @mtkmodel. For the most part, it works like the docs but there are edge cases like this and the other issue you opened.

Can this issue be closed now?

[tpdsantos]

Yes, it answered my question and solved my problem, thank you