Fix scalar @system by converting arguments to matrices

[ueliwechsler]

Thinking about other solutions to handle scalar system in @system.

The problems with the constructor for scalar systems could be fixed by converting the argument with hcat and vcat to a matrix respectively a vector.

Basically, the same we did in the constructor for Number arguments.
Which means, that from the point of the @system macro, the scalar constructor would not be needed.

[mforets]

I like the idea in this PR 👍

My impression is that handling scalars in@system was more problematic than we thought.. I hope we can get to grips with that feature.. or throw it out of the window 😆

NB: I just fixed the conflicts wrt master for the test script, so you may have to git pull on your local branch.

[ueliwechsler]

My impression is that handling scalars in@system was more problematic than we thought

Yes! We did not consider that as a result of having both scalar and matrices there occur corner cases. Therefore, it simplifies if we convert everything to an Array before calling the constructor.
AFAIK, the only place where we don not convert the scalar is

MathematicalSystems.jl/src/macros.jl

Line 412 in d71a284

push!(rhs_params, (array, :A))

[ueliwechsler]

On a different topic. Can I get some help with the doctest? 🙈
doctest(MathematicalSystems, fix=true) does not work for me.

[schillic]

On a different topic. Can I get some help with the doctest? see_no_evil
doctest(MathematicalSystems, fix=true) does not work for me.

Oh yes, I also noticed that at some point. I think the reason is that we do not always write using MathematicalSystems in the doctests.
In conclusion, I think you need to fix them manually (or add this command to the top of each doctest; it can be hidden with # hide I think).

Here is an example from the doctest errors:

│ extract_sum([:(A1*x)], :x, :u, :w)
│ 
│ Evaluated output:
│ 
│ 1-element Array{Tuple{Any,Symbol},1}:
│  (:(hcat(A1)), :A)
│ 
│ Expected output:
│ 
│ 1-element Array{Tuple{Any,Symbol},1}:
│  (:(hcat(:A1)), :A)

Here there is a colon (:) that apparently got removed.

Also notice that when @mforets merged the latest changes here, other tests started breaking.

[ueliwechsler]

Here there is a colon (:) that apparently got removed.

Also notice that when @mforets merged the latest changes here, other tests started breaking.

Thanks a lot. I did not notice it!