diskmargin: drop the delay-margin line from the Diskmargin show method

The printed delay margin was computed as ϕm/ω0 using the disk-margin critical
frequency (the skewed-sensitivity peak). This is not the classical delay margin
(which uses the gain crossover frequency) and, more importantly, is not a valid
lower bound on the destabilizing delay: a delay's phase lag ωτ grows with
frequency, so the binding frequency is wherever ϕm(ω)/ω is smallest, which is
generally not ω0. Evaluating the ratio only at ω0 can therefore overstate the
tolerable delay. Drop the misleading line rather than print a number that reads
as a guarantee but isn't one.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: baggepinnen

Project.toml

@@ -1,7 +1,7 @@
 name = "RobustAndOptimalControl"
 uuid = "21fd56a4-db03-40ee-82ee-a87907bee541"
 authors = ["Fredrik Bagge Carlson", "Marcus Greiff"]
-version = "0.4.50"
+version = "0.4.52"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/diskmargin.jl

@@ -64,14 +64,6 @@ function Base.show(io::IO, dm::Diskmargin)
         println(io, "Gain margins: [$(dm.γmin), $(dm.γmax)]")
     end
     println(io, "Phase margin: ", dm.ϕm)
-    delaymarg = π/180 * dm.ϕm / dm.ω0
-    print(io, "Delay margin: ", delaymarg, " s")
-    if isdiscrete(dm.L)
-        samples = delaymarg / dm.L.Ts
-        println(io, ",  ", isfinite(samples) ? floor(Int, samples) : samples, " samples")
-    else
-        println(io)
-    end
     println(io, "Skew: ", dm.σ)
     println(io, "Worst-case perturbation: ", dm.f0)
 end