Thermostat PID

Adds feedback — backward information flow within a single timestep.

GDS Decomposition

X = (T, E)
U = measured_temp
g = pid_controller
f = update_room
Θ = {setpoint, Kp, Ki, Kd}

Composition

(sensor >> controller >> plant >> update).feedback([
    Energy Cost: plant -> controller CONTRAVARIANT
])

flowchart TD
    Temperature_Sensor([Temperature Sensor]) --> PID_Controller[PID Controller]
    PID_Controller --> Room_Plant[Room Plant]
    Room_Plant --> Update_Room[[Update Room]]
    Room_Plant ==Energy Cost==> PID_Controller

What You'll Learn

• .feedback() composition for within-timestep backward flow
• CONTRAVARIANT flow direction (backward_out → backward_in)
• ControlAction role — reads state and emits control signals
• backward_in / backward_out ports on block interfaces
• Multi-variable Entity (Room has both temperature and energy_consumed)

Key distinction

Room Plant is ControlAction (not Mechanism) because it has backward_out. Mechanisms cannot have backward ports.

Files

• model.py
• test_model.py
• VIEWS.md