Fixing bug with matrix 2x5 mul 5x4

Matrix Math/Models/Matrix.cs

@@ -108,7 +108,7 @@ public Matrix(int sizeX, int sizeY, double defaultValue)
         }
         public static Matrix operator *(Matrix a, Matrix b)
         {
-            if (a.SizeX != b.SizeY)
+            if (a.SizeY != b.SizeX)
                 return null;
 
             Matrix resultMatrix = new Matrix(a.SizeX, b.SizeY);

Matrix_Test/Matrix2x5and5x4.cs

@@ -0,0 +1,34 @@
+using Matrix_Math.Models;
+using Xunit;
+
+namespace Matrix_Test
+{
+    public class Matrix2x5and5x4
+    {
+        private Matrix a = new Matrix(2, 5);
+        private Matrix b = new Matrix(5, 4);
+
+        public Matrix2x5and5x4()
+        {
+            a[0, 0] = 1; a[0, 1] = 2; a[0, 2] = 3; a[0, 3] = 4; a[0, 4] = 5;
+            a[1, 0] = 6; a[1, 1] = 7; a[1, 2] = 8; a[1, 3] = 9; a[1, 4] = 10;
+
+            b[0, 0] = 1; b[0, 1] = 2; b[0, 2] = 3; b[0, 3] = 4;
+            b[1, 0] = 2; b[1, 1] = 3; b[1, 2] = 4; b[1, 3] = 5;
+            b[2, 0] = 3; b[2, 1] = 4; b[2, 2] = 5; b[2, 3] = 6;
+            b[3, 0] = 6; b[3, 1] = 7; b[3, 2] = 7; b[3, 3] = 7;
+            b[4, 0] = 8; b[4, 1] = 9; b[4, 2] = 9; b[4, 3] = 9;
+        }
+        [Fact]
+        public void Mul()
+        {
+            var result = a * b;
+
+            var e = new Matrix(2, 4);
+            e[0, 0] = 78; e[0, 1] = 93; e[0, 2] = 99; e[0, 3] = 105;
+            e[1, 0] = 178; e[1, 1] = 218; e[1, 2] = 239; e[1, 3] = 260;
+
+            Assert.Equal(e, result);
+        }
+    }
+}