interpolation test: added rational behavior contract

Signed-off-by: Christoph Ruegg <git@cdrnet.ch>

src/Managed.UnitTests/InterpolationTests/InterpolationContract.cs

@@ -41,6 +41,7 @@ namespace MathNet.Numerics.UnitTests.InterpolationTests
         public Func<IList<double>, IList<double>, IInterpolation> Factory { get; set; }
         public int[] Order { get; set; }
         public bool PolynomialBehavior { get; set; }
+        public bool RationalBehavior { get; set; }
 
         public InterpolationContract()
         {
@@ -58,6 +59,11 @@ namespace MathNet.Numerics.UnitTests.InterpolationTests
             {
                 yield return CreatePolynomialBehaviorTest("PolynomialBehavior");
             }
+
+            if (RationalBehavior)
+            {
+                yield return CreateRationalBehaviorTest("RationalBehavior");
+            }
         }
 
         private Test CreateFactoryReturnsCorrectTypeTest(string name)
@@ -216,5 +222,56 @@ namespace MathNet.Numerics.UnitTests.InterpolationTests
                 Assert.AreApproximatelyEqual(-5071.0, interpolation.Interpolate(-10.0), 1e-6, "A -10.0");
             });
         }
+
+        private Test CreateRationalBehaviorTest(string name)
+        {
+            return new TestCase(name, () =>
+            {
+                double[] points, values;
+                SampleFunctionEquidistant(t => 1 / (1 + (t * t)), -5.0, 5.0, 41, out points, out values);
+                var interpolation = Factory(points, values);
+
+                for (int i = 0; i < points.Length; i++)
+                {
+                    Assert.AreApproximatelyEqual(
+                        values[i],
+                        interpolation.Interpolate(points[i]),
+                        1e-12,
+                        "Match on knots");
+                }
+
+                double[] testPoints, testValues;
+                SampleFunctionEquidistant(t => 1 / (1 + (t * t)), -5.0, 5.0, 81, out testPoints, out testValues);
+
+                for (int i = 0; i < testPoints.Length; i++)
+                {
+                    Assert.AreApproximatelyEqual(
+                        testValues[i],
+                        interpolation.Interpolate(testPoints[i]),
+                        1e-5,
+                        "Match between knots");
+                }
+            });
+        }
+
+        private static void SampleFunctionEquidistant(
+            Func<double, double> f,
+            double start,
+            double stop,
+            int samples,
+            out double[] points,
+            out double[] values)
+        {
+            points = new double[samples];
+            values = new double[samples];
+
+            double step = (stop - start) / (samples - 1);
+            for (int i = 0; i < points.Length; i++)
+            {
+                double t = start + (i * step);
+                points[i] = t;
+                values[i] = f(t);
+            }
+        }
     }
 }

src/Managed.UnitTests/InterpolationTests/InterpolationTest.cs

@@ -42,7 +42,8 @@ namespace MathNet.Numerics.UnitTests.InterpolationTests
         {
             Factory = Interpolation.CreateLinearBetweenPoints,
             Order = new[] { 2, 3, 6 },
-            PolynomialBehavior = false
+            PolynomialBehavior = false,
+            RationalBehavior = false
         };
 
         [VerifyContract]
@@ -50,7 +51,8 @@ namespace MathNet.Numerics.UnitTests.InterpolationTests
         {
             Factory = Interpolation.CreateRationalPoleFree,
             Order = new[] { 1, 2, 6 },
-            PolynomialBehavior = true
+            PolynomialBehavior = true,
+            RationalBehavior = true
         };
 
         [VerifyContract]
@@ -58,7 +60,8 @@ namespace MathNet.Numerics.UnitTests.InterpolationTests
         {
             Factory = (t, x) => new NevillePolynomialInterpolation(t, x),
             Order = new[] { 1, 2, 6 },
-            PolynomialBehavior = true
+            PolynomialBehavior = true,
+            RationalBehavior = false
         };
     }
 }