From fdfb85f69536c8c1aa9975746d63ed17dcdb0285 Mon Sep 17 00:00:00 2001
From: Tyler Veness <calcmogul@gmail.com>
Date: Sat, 17 Sep 2022 00:18:08 -0700
Subject: [PATCH] [wpimath] Remove Java LQR constructor that takes a controller
 gain matrix (#4419)

The controller gain matrix K should be computed from the solution to the
DARE, but this constructor does not do that. It effectively violates a
postcondition enforced by the other constructors by letting the user
throw in a controller gain matrix that didn't come from an LQR.

Removing this constructor is a breaking change, but it never should have
been included in the class in the first place. There's also no valid
reason to use it. I assume it was originally added for debugging the
class internals.

This constructor does not exist in C++.
---
 .../controller/LinearQuadraticRegulator.java  | 19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/wpimath/src/main/java/edu/wpi/first/math/controller/LinearQuadraticRegulator.java b/wpimath/src/main/java/edu/wpi/first/math/controller/LinearQuadraticRegulator.java
index 7f16576bcf..190cd2a678 100644
--- a/wpimath/src/main/java/edu/wpi/first/math/controller/LinearQuadraticRegulator.java
+++ b/wpimath/src/main/java/edu/wpi/first/math/controller/LinearQuadraticRegulator.java
@@ -7,7 +7,6 @@ package edu.wpi.first.math.controller;
 import edu.wpi.first.math.Drake;
 import edu.wpi.first.math.MathSharedStore;
 import edu.wpi.first.math.Matrix;
-import edu.wpi.first.math.Nat;
 import edu.wpi.first.math.Num;
 import edu.wpi.first.math.StateSpaceUtil;
 import edu.wpi.first.math.Vector;
@@ -175,24 +174,6 @@ public class LinearQuadraticRegulator<States extends Num, Inputs extends Num, Ou
     reset();
   }
 
-  /**
-   * Constructs a controller with the given coefficients and plant.
-   *
-   * @param states The number of states.
-   * @param inputs The number of inputs.
-   * @param k The gain matrix.
-   */
-  @SuppressWarnings("ParameterName")
-  public LinearQuadraticRegulator(
-      Nat<States> states, Nat<Inputs> inputs, Matrix<Inputs, States> k) {
-    m_K = k;
-
-    m_r = new Matrix<>(states, Nat.N1());
-    m_u = new Matrix<>(inputs, Nat.N1());
-
-    reset();
-  }
-
   /**
    * Returns the control input vector u.
    *