Auxiliary variable in MTK connector

Specific Domains Modelling & Simulations
1

Consider the MTK Pin example.

@connector Pin begin
    v(t) = 0.0, [description = "Voltage"]
    i(t), [connect = Flow]
end

Suppose I wanted to also define the auxiliary variable p(t) = v * i (for power), such that I could refer to pin.p. I can’t figure out how to do that. The docs for connector say that connectors can be complex:

Similar to @mtkmodel, @connector accepts begin blocks of @components, @equations, @extend, @parameters, @structural_parameters, @variables.

But @variables seems to be a no-op (same effect as when defining directly with @variables).

@connector Pin begin
    v(t) = 0.0, [description = "Voltage"]
    i(t), [connect = Flow]
    p(t), [connect = Flow]
    @equations begin
       p = v * i
    end
end

seems to work, but

  • A) It yields a warning about unbalanced connectors
  • B) It will generate a lot of redundant connecting equations. p really is an auxiliary variable, no need to “connect” it (and I shouldn’t have to specify its connect property)
2

Try

p(t), [output = true]

instead, this indicates that p is a computed variable and I believe this should remove the warnings about unbalanced connectors.

1 Like
3

If I am not mistaken

p(t), [connect = Stream]

should do the job.
(At least according to the doc: Symbolic Metadata · ModelingToolkit.jl)