Use unicode characters in docs equations (#3487)

javac and javadoc needed the encoding set to UTF-8.

wpimath/src/test/java/edu/wpi/first/math/estimator/KalmanFilterTest.java

@@ -45,8 +45,8 @@ public class KalmanFilterTest {
     elevatorPlant = LinearSystemId.createElevatorSystem(motors, m, r, G);
   }
 
-  // A swerve drive system where the states are [x, y, theta, vx, vy, vTheta]^T,
-  // Y is [x, y, theta]^T and u is [ax, ay, alpha}^T
+  // A swerve drive system where the states are [x, y, theta, vx, vy, vTheta]ᵀ,
+  // Y is [x, y, theta]ᵀ and u is [ax, ay, alpha}ᵀ
   LinearSystem<N6, N3, N3> m_swerveObserverSystem =
       new LinearSystem<>(
           Matrix.mat(Nat.N6(), Nat.N6())

wpimath/src/test/java/edu/wpi/first/math/system/DiscretizationTest.java

@@ -58,8 +58,9 @@ public class DiscretizationTest {
     assertEquals(x1Truth, x1Discrete);
   }
 
-  // Test that the discrete approximation of Q is roughly equal to
-  // integral from 0 to dt of e^(A tau) Q e^(A.T tau) dtau
+  //                                             dt
+  // Test that the discrete approximation of Q ≈ ∫ e^(Aτ) Q e^(Aᵀτ) dτ
+  //                                             0
   @Test
   public void testDiscretizeSlowModelAQ() {
     final var contA = new MatBuilder<>(Nat.N2(), Nat.N2()).fill(0, 1, 0, 0);
@@ -86,8 +87,9 @@ public class DiscretizationTest {
             + discQIntegrated);
   }
 
-  // Test that the discrete approximation of Q is roughly equal to
-  // integral from 0 to dt of e^(A tau) Q e^(A.T tau) dtau
+  //                                             dt
+  // Test that the discrete approximation of Q ≈ ∫ e^(Aτ) Q e^(Aᵀτ) dτ
+  //                                             0
   @Test
   public void testDiscretizeFastModelAQ() {
     final var contA = new MatBuilder<>(Nat.N2(), Nat.N2()).fill(0, 1, 0, -1406.29);