CAD.1:4.1 - Formulate the unsplit question

State the controlled quantities, objective or preference, hard constraints, operating domain, relevant disturbances, measurements and available actions. Distinguish three time quantities: the dynamics and disturbance times, the horizon over which a choice matters, and the time needed to obtain and execute that choice. A fast update is useful only if observations, computation and actuation support it.

Use a centralized mathematical formulation when it helps reveal coupling, even if that formulation is too expensive to run. It can be a finite-horizon objective with dynamics and constraints, a reach-and-avoid problem, or a reference-following requirement. It is the common comparison basis, not a promise that one optimizer must solve everything.

Retain a feasible simple controller as a baseline where available. State what it cannot achieve at acceptable effort: for example obstacle look-ahead, preview-dependent economy or long-horizon allocation. If the baseline’s actual limitation is unknown, test that uncertainty before adding layers.

When a qualified existing loop has adequate tracking and disturbance rejection but requested commands violate constraints, compare adding a reference or command governor before redesigning that loop. Use the joint plant-controller model, admissible initial conditions and qualified command-update rule described in CAD.Reference:4.5.1. Check whether the resulting command delay or distortion still meets the task. If it does, retain that candidate; if it does not, identify the unmet requirement that a different interface, planner or controller must address.