Distributions: test for Weibull.Estimate #339

src/Numerics/Distributions/Weibull.cs

@@ -429,7 +429,7 @@ namespace MathNet.Numerics.Distributions
         public static Weibull Estimate(IEnumerable<double> samples, System.Random randomSource = null)
         {
             var samp = samples as double[] ?? samples.ToArray();
-            double n = samp.Count(), s1 = 0, s2 = 0, s3 = 0, previousC = Int32.MinValue, QofC = 0;
+            double n = samp.Length, s1 = 0, s2 = 0, s3 = 0, previousC = Int32.MinValue, QofC = 0;
 
             if (n <= 1) throw new Exception("Observations not sufficient");
 
@@ -455,8 +455,12 @@ namespace MathNet.Numerics.Distributions
             }
 
             foreach (double x in samp)
+            {
                 if (x > 0)
+                {
                     b += Math.Pow(x, c);
+                }
+            }
 
             b = Math.Pow(b / n, 1 / c);
 

src/UnitTests/DistributionTests/Continuous/WeibullTests.cs

@@ -336,5 +336,22 @@ namespace MathNet.Numerics.UnitTests.DistributionTests.Continuous
             var n = new Weibull(shape, scale);
             AssertHelpers.AlmostEqualRelative(cdf, n.CumulativeDistribution(x), 14);
         }
+
+        /// <summary>
+        /// Can estimate distribution parameters.
+        /// </summary>
+        [TestCase(1.0, 0.1)]
+        [TestCase(1.0, 1.0)]
+        [TestCase(10.0, 1.0)]
+        [TestCase(10.0, 10.0)]
+        [TestCase(10.0, 50.0)]
+        public void CanEstimateParameters(double shape, double scale)
+        {
+            var original = new Weibull(shape, scale, new Random(100));
+            var estimated = Weibull.Estimate(original.Samples().Take(10000));
+
+            AssertHelpers.AlmostEqualRelative(shape, estimated.Shape, 1);
+            AssertHelpers.AlmostEqualRelative(scale, estimated.Scale, 1);
+        }
     }
 }