Fixed a rounding bug in the Matrix GetHashCode that would cause matrices that were deemed equal to not have the same hash code

Skills/Numerics/Matrix.cs

@@ -9,6 +9,10 @@ namespace Moserware.Numerics
     /// </summary>    
     internal class Matrix
     {
+        // Anything smaller than this will be assumed to be rounding error in terms of equality matching
+        private const int FractionalDigitsToRoundTo = 10;
+        private static readonly double ErrorTolerance = Math.Pow(0.1, FractionalDigitsToRoundTo); // e.g. 1/10^10
+
         protected double[][] _MatrixRowValues;
         // Note: some properties like Determinant, Inverse, etc are properties instead
         // of methods to make the syntax look nicer even though this sort of goes against
@@ -387,8 +391,6 @@ namespace Moserware.Numerics
                 return false;
             }
             
-            const double errorTolerance = 0.0000000000001;
-
             for (int currentRow = 0; currentRow < a.Rows; currentRow++)
             {
                 for (int currentColumn = 0; currentColumn < a.Columns; currentColumn++)
@@ -397,7 +399,7 @@ namespace Moserware.Numerics
                         Math.Abs(a._MatrixRowValues[currentRow][currentColumn] -
                                  b._MatrixRowValues[currentRow][currentColumn]);
 
-                    if (delta > errorTolerance)
+                    if (delta > ErrorTolerance)
                     {
                         return false;
                     }
@@ -426,7 +428,9 @@ namespace Moserware.Numerics
 
                     for (int currentColumn = 0; currentColumn < Columns; currentColumn++)
                     {
-                        result += multiplier*_MatrixRowValues[currentRow][currentColumn];
+                        double cellValue = _MatrixRowValues[currentRow][currentColumn];
+                        double roundedValue = Math.Round(cellValue, FractionalDigitsToRoundTo);
+                        result += multiplier*roundedValue;
                     }
                 }
             }

UnitTests/Numerics/MatrixTests.cs

@@ -121,6 +121,16 @@ namespace UnitTests.Numerics
             Assert.AreEqual(d, f);
             Assert.AreEqual(d.GetHashCode(), f.GetHashCode());
 
+            // Test rounding (thanks to nsp on GitHub for finding this case)
+            var g = new SquareMatrix(1, 2.00000000000001,
+                                     3, 4);
+
+            var h = new SquareMatrix(1, 2,
+                                     3, 4);
+
+            Assert.IsTrue(g == h);
+            Assert.AreEqual(g, h);
+            Assert.AreEqual(g.GetHashCode(), h.GetHashCode());
         }
 
         [Test]