Nixed mirrorAngleOrigin because it's not correct.

The correct way to mirror an angle in [-PI, PI] around the x-axis is simply to
negate it, which doesn't seem ceremonious enough to require a utility method.

src/main/java/pythagoras/d/MathUtil.java

@@ -174,15 +174,6 @@ public class MathUtil
         return (a > 0f ? Math.PI : -Math.PI) - a;
     }
 
-    /**
-     * Returns the mirror angle of the specified angle (assumed to be in [-pi, +pi]). The angle is
-     * mirrored around the origin (zero degrees). One can visualize this as mirroring around the
-     * "x-axis".
-     */
-    public static double mirrorAngleOrigin (double a) {
-        return a + (a > 0f ? -Math.PI : Math.PI);
-    }
-
     /**
      * Sets the number of decimal places to show when formatting values. By default, they are
      * formatted to three decimal places.

src/main/java/pythagoras/f/MathUtil.java

@@ -174,15 +174,6 @@ public class MathUtil
         return (a > 0f ? FloatMath.PI : -FloatMath.PI) - a;
     }
 
-    /**
-     * Returns the mirror angle of the specified angle (assumed to be in [-pi, +pi]). The angle is
-     * mirrored around the origin (zero degrees). One can visualize this as mirroring around the
-     * "x-axis".
-     */
-    public static float mirrorAngleOrigin (float a) {
-        return a + (a > 0f ? -FloatMath.PI : FloatMath.PI);
-    }
-
     /**
      * Sets the number of decimal places to show when formatting values. By default, they are
      * formatted to three decimal places.

src/test/java/pythagoras/f/MathUtilTest.java

@@ -30,9 +30,4 @@ public class MathUtilTest
 
         assertEquals(MathUtil.lerpa(3*PI4, -3*PI4, 0.5f), -PI, MathUtil.EPSILON);
     }
-
-    @Test public void testMirrorAngleOrigin() {
-        assertEquals(-PI2, MathUtil.mirrorAngleOrigin(PI2), MathUtil.EPSILON);
-        assertEquals(PI2, MathUtil.mirrorAngleOrigin(-PI2), MathUtil.EPSILON);
-    }
 }