How to interface between functional and macro syntax in MTK

Specific Domains Modelling & Simulations
1

How does one pass structural parameters from a @mtkmodel to a @component function? Is it possible to sort of convert between the positional syntax of @component function to the keyword syntax of @mtkmodel (for structural parameters)? As an example, how would one do the following?

@component function Subsystem(B; d, name)

    vars = @variables begin
        (y(t))[1:B]
    end

    eqs = [
        D(y) ~ d*y
    ]

    ODESystem(eqs, t, vars, eqs; name)
end

@mtkmodel Example2 begin
    
    @structural_parameters begin
        A = 1
        B = 2
    end

    @parameters begin
        c
        d
    end

    @components begin
        subsystem = Subsystem(B; d=d)
    end
end

A = 10
B = 20
c = 4.67
d = 2.34

@mtkbuild correct_method = Example2(A=A, B=B, c=c, d=d)

MethodError: no method matching Subsystem(; B::Int64, name::Symbol, d::Num)
The function Subsystem exists, but no method is defined for this combination of argument types.

Closest candidates are:
Subsystem(::Any; d, name) got unsupported keyword argument “B”
@ Main C:\Users\matth.julia\packages\ModelingToolkit\Ljerk\src\systems\abstractsystem.jl:2461

Stacktrace:
[1] macro expansion
@ C:\Users\matth.julia\packages\ModelingToolkit\Ljerk\src\systems\abstractsystem.jl:2295 [inlined]
[2] Example2(; name::Symbol, A::Int64, B::Int64, c::Float64, d::Float64, subsystem__d::Nothing, subsystem__B::Nothing)
@ Main C:\Users\matth.julia\packages\ModelingToolkit\Ljerk\src\systems\model_parsing.jl:1203
[3] (::ModelingToolkit.Model{typeof(Example2), Dict{Symbol, Any}})(; kw::@Kwargs{name::Symbol, A::Int64, B::Int64, c::Float64, d::Float64})
@ ModelingToolkit C:\Users\matth.julia\packages\ModelingToolkit\Ljerk\src\systems\model_parsing.jl:25
[4] top-level scope
@ C:\Users\matth.julia\packages\ModelingToolkit\Ljerk\src\systems\abstractsystem.jl:2295

2

You have B as a positional argument, not a keyword argument. The macro requires it to be a keyword argument.

3

But B needs to be a positional argument in Subsystem, so that it is defined as a non-symbolic parameter, right? So how to have B (non-symbolic parameter) as positional for @component function Subsystem, but keyword when calling it in macro?

Also being discussed here: Interpolations component cannot be used within @mtkmodel macro · Issue #340 · SciML/ModelingToolkitStandardLibrary.jl · GitHub

4

Why not just make it a keyword argument?

5

Thank you Chris.