diskmargin: drop the delay-margin line from show#152
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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>
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Motivation
show(::Diskmargin)printed a delay margin computed asϕm/ω0, whereω0is the disk-margin critical frequency (the skewed-sensitivity peak).This is misleading:
ω_gc. For a disk margin there is no clean gain crossover, andω0 ≠ ω_gcin general.ωτgrows linearly with frequency, so the binding frequency is whereverϕm(ω)/ωis smallest — generally notω0. Evaluating the ratio only atω0can overstate the tolerable delay.A genuine lower bound would be
min_ω ϕm(ω)/ω, which requires the frequency-dependent disk margin rather than the single critical-frequency value. Rather than print a number that reads as a guarantee but isn't one, this PR drops the line. A properdelaymarginbased on the frequency sweep can be added later if wanted.Change
Remove the "Delay margin" (and discrete "samples") output from
Base.show(::Diskmargin). No tests or docs depend on it.🤖 Generated with Claude Code