`margin` throws an error when the system has delay

[ronisbr]

Consider the following system:

julia> C = 0.6 + 30 * tf([1, 0], [1])

julia> G = tf([0.04, 0.0001, 1.1], [1, 0.03, 254.9])

julia> H = tf([0.25], [1, 1, 0.25])

julia> L = C * G * H * delay(1)

If I try to obtain the margins using allMargins = false, I get the following error:

julia> margin(L)
ERROR: BoundsError: attempt to access 1-element Vector{Float64} at index [3]
Stacktrace:
 [1] throw_boundserror(A::Vector{Float64}, I::Tuple{Int64})
   @ Base ./essentials.jl:14
 [2] getindex
   @ ./essentials.jl:916 [inlined]
 [3] sisomargin(sys::DelayLtiSystem{Float64, Float64}, w::Vector{Float64}; full::Bool, allMargins::Bool)
   @ ControlSystemsBase ~/.julia/packages/ControlSystemsBase/kvrre/src/analysis.jl:463
 [4] sisomargin
   @ ~/.julia/packages/ControlSystemsBase/kvrre/src/analysis.jl:444 [inlined]
 [5] margin(sys::DelayLtiSystem{Float64, Float64}, w::Vector{Float64}; full::Bool, allMargins::Bool)
   @ ControlSystemsBase ~/.julia/packages/ControlSystemsBase/kvrre/src/analysis.jl:429
 [6] margin
   @ ~/.julia/packages/ControlSystemsBase/kvrre/src/analysis.jl:410 [inlined]
 [7] margin(system::DelayLtiSystem{Float64, Float64})
   @ ControlSystemsBase ~/.julia/packages/ControlSystemsBase/kvrre/src/analysis.jl:485
 [8] top-level scope
   @ REPL[12]:1

If works if I remove the delay or if I set allMargins = true:

julia> margin(L, allMargins = true)
(wgm = [[2.041402041527457, 11.081144646232188, 20.471831757852467, 26.741832375445096, 33.017521326540425, 39.2956993185886, 45.57529664743531, 51.85576981114693, 58.136836945502154, 64.41832383251091  …  263.7340285648331, 305.9620408928975, 347.7262613229265, 398.77747116198157, 429.0787275370144, 555.4392133863881, 566.1520203618901, 645.6860901815029, 661.8552898282388, 945.0001606654438];;], gm = [[77.50590739230606, 51.31234174534322, 28.63000544588986, 59.6816713967569, 86.52667289853684, 111.36432002593598, 135.07896681048322, 158.09878255883388, 180.65767674302057, 202.89464702435197  …  876.241336647831, 1017.3980298848596, 1156.9095606216863, 1327.3591877600206, 1428.4975273095072, 1850.1007378722575, 1885.8358956515124, 2151.1142359545875, 2205.040221748687, 3149.1992770654497];;], wpm = [Float64[];;], pm = [Float64[];;])

[baggepinnen]

Thanks for the issue, it should be fixed by

• fix #941 #942

[ronisbr]

Awesome! Thanks for the quick response @baggepinnen !