Array operations inside @equations macro

[matthew-kapp]

Question❓

Am I correct that array operations are not supported within the @mtkmodel macro yet? If not, is it planned to do so?

According to the docs it only mentions support for parameters and variables [https://docs.sciml.ai/ModelingToolkit/stable/basics/MTKLanguage/#Different-ways-to-define-symbolics-arrays:], so I assume it's not supported yet. Also, if I use for example, it works:

eqs =[
    [h[i] ~ h[i-1] + Q̇[i-1]/ṁ for i in 2:N_elements]
    ]

but this does not work:

@equations begin
    [h[i] ~ h[i-1] + Q̇[i-1]/ṁ for i in 2:N_elements]
 end

[ChrisRackauckas]

You can use broadcast for these expressions?

[cstjean]

Splatting works for us.

@equations begin
    [h[i] ~ h[i-1] + Q̇[i-1]/ṁ for i in 2:N_elements]...
 end

[cstjean]

Aside: One thing that I appreciate about MTK is that it goes to such great lengths to support a macro-free workflow where I can write things like derivative_eq = D(x) ~ x * t. I dig that! But then the @mtkmodel macro is the complete opposite, with super heavy macro analysis, such that anything that isn't explicitly supported fails. Eg.

@components begin
    tanks = [WaterTank() for i in 1:2]  # works!
    tanks = [WaterTank(), WaterTank()]   # Fails. Somebody has to write a PR for that.
end

As a user, this isn't pleasant. It looks like the RHS should be plain Julia code, but instead I keep falling into DSL sink-holes. And as a library, it means that the macro will have to keep growing and growing to support all use cases.

In my mind, tanks = whatever should macroexpand into process_component(whatever, name=:tanks). Methods like process_component(::Vector; name) = ... can handle the various possible right-hand-sides so much more elegantly than macro parsing can. And the user gets referential transparency back.

Some changes would have to be done like allowing WaterTank() without a name kwarg (defaulting to unnamed), but IMO that would be worth it.

/rant

[matthew-kapp]

Ah you need to add the 3 dots. Is that called splatting?