Class LinearSystemLoop<States extends Num,​Inputs extends Num,​Outputs extends Num>

java.lang.Object
edu.wpi.first.math.system.LinearSystemLoop<States,​Inputs,​Outputs>
Type Parameters:
States - Number of states.
Inputs - Number of inputs.
Outputs - Number of outputs.

public class LinearSystemLoop<States extends Num,​Inputs extends Num,​Outputs extends Num>
extends Object
Combines a controller, feedforward, and observer for controlling a mechanism with full state feedback.

For everything in this file, "inputs" and "outputs" are defined from the perspective of the plant. This means U is an input and Y is an output (because you give the plant U (powers) and it gives you back a Y (sensor values)). This is the opposite of what they mean from the perspective of the controller (U is an output because that's what goes to the motors and Y is an input because that's what comes back from the sensors).

For more on the underlying math, read https://file.tavsys.net/control/controls-engineering-in-frc.pdf.