Merge pull request mathnet#1072 from jkalias/master

Fix SpecialFunctions.Hypotenuse when elements are double.NaN

Author: cdrnet

src/Numerics.Tests/SpecialFunctionsTests/SpecialFunctionsTests.cs

@@ -332,5 +332,18 @@ public void Log1p(double x, double y)
         {
             AssertHelpers.AlmostEqualRelative(y, SpecialFunctions.Log1p(x), 14);
         }
+
+        [Test]
+        public void HypotenuseWhenArgumentIsNanReturnesNan()
+        {
+            Assert.True(double.IsNaN(SpecialFunctions.Hypotenuse(double.NaN, 0)));
+        }
+
+        [Test]
+        public void L2NormOfVectorWhenElementsNanReturnsNan()
+        {
+            var v = LinearAlgebra.Vector<double>.Build.Dense(new[] { double.NaN, 0 });
+            Assert.True(double.IsNaN(v.L2Norm()));
+        }
     }
 }

src/Numerics/SpecialFunctions/Stability.cs

@@ -91,6 +91,11 @@ public static Complex32 Hypotenuse(Complex32 a, Complex32 b)
         /// <returns>Returns <code>sqrt(a<sup>2</sup> + b<sup>2</sup>)</code> without underflow/overflow.</returns>
         public static double Hypotenuse(double a, double b)
         {
+            if (double.IsNaN(a) || double.IsNaN(b))
+            {
+                return double.NaN;
+            }
+
             if (Math.Abs(a) > Math.Abs(b))
             {
                 double r = b/a;