Revisiting old code: was there ever an `LTISystem` composed type in `ControlSystems.jl`?

[B-LIE]

I'm revisiting some Julia code I worked with during early Covid (first half of 2020). In my code, I import ControlSystems.jl, and create a struct as:

struct MFD{T} <: LTISystem
    N::Matrix{Poly{T}}
    D::Matrix{Poly{T}}
...
end

My code doesn't work anymore. That is ok, but I'm just wondering whether LTISystem was part of ControlSystems.jl back then, and whether that type has been moved to some other package (or replaced with something else).

[baggepinnen]

I believe it's in ControlSystemsBase

[B-LIE]

Thanks -- I found it. It is exported from ControlSystemsBase, and is defined as:

abstract type LTISystem{TE<:TimeEvolution} <: AbstractSystem end

I suspect it has changed since I used it 4 1/2 years ago, in that it seems to require that parameters are of type TimeEvolution. I used it for transfer matrices/matrix fraction descripton.