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Root locus: relative step-size control, improper systems, default gain and plot limits #1079

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Merged
baggepinnen merged 3 commits into from
Oct 8, 2026
Merged

Root locus: relative step-size control, improper systems, default gain and plot limits #1079

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e5cba84
Measure the step size of the root locus relative to the pole magnitude
baggepinnen Oct 8, 2026
3ae219b
Support improper transfer functions in the root locus
baggepinnen Oct 8, 2026
ef110c5
Choose the default root-locus gain and plot limits from the open-loop…
baggepinnen Oct 8, 2026
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18 changes: 13 additions & 5 deletions lib/ControlSystemsBase/ext/ControlSystemsBaseMakieExt.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -517,7 +517,7 @@ function CSMakie.rlocusplot(args...; kwargs...)
fig = Figure()
CSMakie.rlocusplot!(fig, args...; kwargs...)
end
function CSMakie.rlocusplot!(fig, P::LTISystem, K=500; output=false, kwargs...)
function CSMakie.rlocusplot!(fig, P::LTISystem, K=nothing; output=false, kwargs...)
# Compute root locus
result = rlocus(P, K; output=output)
roots, Z, K_vals = result.roots, result.Z, result.K
Expand All @@ -533,10 +533,14 @@ function CSMakie.rlocusplot!(fig, P::LTISystem, K=500; output=false, kwargs...)
# Add grid at zero
vlines!(ax, 0, color=:gray, alpha=0.3, linewidth=0.5)
hlines!(ax, 0, color=:gray, alpha=0.3, linewidth=0.5)

if isdiscrete(P)
ϕ = range(0, 2π, length=200)
lines!(ax, cos.(ϕ), sin.(ϕ), color=:gray, linestyle=:dash)
end

redata = real.(roots)
imdata = imag.(roots)

# Plot root locus branches
for i in 1:size(redata, 2)
lines!(ax, redata[:, i], imdata[:, i], color=:blue)
Expand All @@ -551,7 +555,8 @@ function CSMakie.rlocusplot!(fig, P::LTISystem, K=500; output=false, kwargs...)
end

# Plot open-loop poles
scatter!(ax, redata[1, :], imdata[1, :],
ol_poles = poles(result.sys)
scatter!(ax, real.(ol_poles), imag.(ol_poles),
marker=:xcross, markersize=10,
color=:red, label="Open-loop poles")

Expand All @@ -561,7 +566,10 @@ function CSMakie.rlocusplot!(fig, P::LTISystem, K=500; output=false, kwargs...)
marker=:diamond, markersize=10,
color=:purple, label="Closed-loop poles")
end


xl, yl = ControlSystemsBase.rlocus_limits(result)
limits!(ax, xl..., yl...)

return fig
end

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