CAD.4:11 - SoTA-Echoing

What should change when a complete control arrangement misses its demand or resource limit? The selected line compares coupled architecture and tuning choices, while retaining a qualified fixed loop with local command modification as a serious alternative. It adopts the joint-choice formulation in Verhoek, Stamouli, Pappas and Matni, 2026 preprint, §§3–7: model dimensions, sampling ratios, horizons and controller parameters affect the same feasibility problem. That construction fixes a two-layer LTI setting and specified delay and controller classes; efficient general optimization remains open. Sections :4.1–4.4 adapt the comparison to a bounded candidate search and require implementation timing rather than treating a computation-cost proxy as a deadline bound. The gain is avoiding incompatible local optima; the cost is a larger search and repeated qualification of coupled choices.

When the lower loop already has the required local performance, first compare changing its command admission or solver. Garone and Kolmanovsky, §§3–4 and Algorithm 1 develop command-governor logic permitting inexact optimization and a non-invariant inner admissible set, with stated feasibility and progress conditions. Adopt the separation between accepting a computed command and merely obtaining a solver output in :4.3; neither an arbitrary partial iterate nor an unqualified hold inherits that result. This can be preferable to buying faster computation or redesigning the tracker, but command progress and admissible-set computation remain costs to compare.

Switching among existing controllers is also a genuine architectural alternative. Wang, Di Cairano and Sanfelice, 2024, §§III–V combine mode-specific admissible sets with explicit switching and Lyapunov conditions. Adapt that comparison when a fast transient and a less oscillatory final approach favor different controllers; carry the guards and transitions into :4.2 and CAD.3:4.1. Separate stable modes alone do not supply the switched guarantee. Reopen the choice when task demand, computing interference or the cost of maintaining those mode conditions changes.