Adapt port based on state

Suppose I am using the PIDController class and I want to update the "object" being pid controlled based on the state of a DiscreteLeafSystem which is changing periodically over time.

For example, suppose I randomly sample an object index from 1-10 every 1 second, and I want a single PIDController that pulls the sampled object to a setpoint.

How do I do this?

Since the object to be controlled by the PIDController class is passed in via an input port, my question seems to boil down to: how do we adaptively rewire input ports to a LeafSystem (PIDController in this case) based on a discrete-time state?

You can't dynamically rewire, but you can use PortSwitch to wire up the appropriate logic.

But in this particular case, I would think that it would be easier to write your own little LeafSystem which take the entire MultibodyPlant state as input and outputs the entire MultibodyPlant actuation as output. This system should put out zero for the actuation values that are not being controller, and implement the PID for the ones that are.

In python, you can now use e.g.

ActuatorView = namedview("actuators", plant.GetActuatorNames())
view = ActuatorView.Zeros()
view.myinstance_myactuator = value

to help with the assignment into the state and actuation vectors.