A couple more maths functions

Source/OpenTK/Math/Matrix4.cs

@@ -280,6 +280,17 @@ namespace OpenTK
             Row2.Xyz = Row2.Xyz.Normalized();
         }
 
+        /// <summary>
+        /// Returns an inverted copy of this instance.
+        /// </summary>
+        public Matrix4 Inverted()
+        {
+            Matrix4 m = this;
+            if (m.Determinant != 0)
+                m.Invert();
+            return m;
+        }
+
         /// <summary>
         /// Gets the translation component of this instance.
         /// </summary>
@@ -343,7 +354,8 @@ namespace OpenTK
                     q.Y = (float)((Row2[1] + Row1[2]) * sq);
                 }
 
-                return q.Normalized();
+                q.Normalize();
+				return q;
             }
         }
 

Source/OpenTK/Math/Quaternion.cs

@@ -192,7 +192,6 @@ namespace OpenTK
         /// <summary>
         /// Returns a copy of the Quaternion scaled to unit length.
         /// </summary>
-        /// <returns></returns>
         public Quaternion Normalized()
         {
             Quaternion q = this;
@@ -200,6 +199,18 @@ namespace OpenTK
             return q;
         }
 
+        public void Invert()
+        {
+            W = -W;
+        }
+
+        public Quaternion Inverted()
+        {
+            var q = this;
+            q.Invert();
+            return q;
+        }
+
         #region public void Normalize()
 
         /// <summary>