Wrong names propagated after matrix multiplication

[baggepinnen]

Here I have two matrices with names (y1, u1) and (y2, u2). When multiplying them, it appears as if the names in the result are chosen based on the second argument only, but I expected to get (y1, u2) when multiplying (y1, u1) * (y2, u2). Maybe my understanding is incorrect?

julia> s1.D
1×1 ComponentMatrix{Int64} with axes Axis(y1 = 1,) × Axis(u1 = 1,)
 1

julia> s2.D
1×1 ComponentMatrix{Int64} with axes Axis(y2 = 1,) × Axis(u2 = 1,)
 1

julia> s1.D*s2.D
1×1 ComponentMatrix{Int64} with axes Axis(y2 = 1,) × Axis(u2 = 1,)
 1

julia> s2.D*s1.D
1×1 ComponentMatrix{Int64} with axes Axis(y1 = 1,) × Axis(u1 = 1,)
 1

[jonniedie]

A colleague of mine was just asking the other day if ControlSystems.jl had named states/inputs/outputs for state space objects like MATLAB has. I told him we could probably make that work with ControlSystems + ComponentArrays, but kinda forgot to pursue it after that.

But yeah, it looks there need to be explicit matrix and vector multiplication methods for ComponentArrays. I used to have them, but type ambiguities when multiplying with other array types got so bad, that I got rid of all *, /, and \ methods in favor of plain broadcasting. But I don't think the broadcasting mechanism can handle matrix multiplication properly, so I'll add in some methods.

[baggepinnen]

I'm working on just that, state-space objects with named states, inputs and outputs. It's kind of hopeless to remember the order of states, in particular when concatenating several systems together. It appears as if it's going to require quite a number of custom methods though, in ControlSystems.jl we have in general been careful with the element types, but not the array types. We thus do a lot of concatenation with zeros(T, n, m) which leaves named components behind :/
As long as the hcat,vcat, +,-,* operations are working, as well as perhaps lsim, freqresp I think we're generally at a place where it becomes useful. If nothing else, one can just ask for the indices from the statespace type and use those to index into any array that represents states/control/outputs.