LA: Unit test to confirm issue #35

src/UnitTests/LinearAlgebraTests/Double/DiagonalMatrixTests.cs

@@ -641,5 +641,29 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double
                 }
             }
         }
+
+        [Test]
+        public void CanGetSubMatrix_Issue35()
+        {
+            // [ 1 0 0 ]
+            // [ 0 2 0 ]
+            // [ 0 0 3 ]
+            var diagMatrix = new DiagonalMatrix(3);
+            for (int i = 0; i < 3; i++)
+            {
+                diagMatrix[i, i] = i + 1;
+            }
+
+            // [ 0 0 ]
+            // [ 2 0 ]
+            var subM2 = diagMatrix.SubMatrix(0, 2, 1, 2);
+            Assert.IsTrue(subM2.Equals(new DenseMatrix(2, 2, new[] {0d, 2d, 0d, 0d})));
+
+            // [ 0 0 ]
+            // [ 2 0 ]
+            // [ 0 3 ]
+            var subM3 = diagMatrix.SubMatrix(0, 3, 1, 2);
+            Assert.IsTrue(subM3.Equals(new DenseMatrix(3, 2, new[] { 0d, 2d, 0d, 0d, 0d, 3d })));
+        }
     }
 }