Added Logit and Logistic functions.

Signed-off-by: jvangael <jurgen.vangael@gmail.com>

src/Numerics/Properties/Resources.Designer.cs

@@ -1,7 +1,7 @@
 //------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated by a tool.
-//     Runtime Version:2.0.50727.4016
+//     Runtime Version:2.0.50727.4200
 //
 //     Changes to this file may cause incorrect behavior and will be lost if
 //     the code is regenerated.
@@ -60,6 +60,15 @@ namespace MathNet.Numerics.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to The argument must be between 0 and 1..
+        /// </summary>
+        internal static string ArgumentBetween0And1 {
+            get {
+                return ResourceManager.GetString("ArgumentBetween0And1", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Value cannot be in the range -1 &lt; x &lt; 1..
         /// </summary>

src/Numerics/Properties/Resources.resx

@@ -282,4 +282,7 @@
   <data name="MatrixRowsOrColumnsMustBePositive" xml:space="preserve">
     <value>The number of rows or columns of a matrix must be positive.</value>
   </data>
+  <data name="ArgumentBetween0And1" xml:space="preserve">
+    <value>The argument must be between 0 and 1.</value>
+  </data>
 </root>

src/Numerics/SpecialFunctions.cs

@@ -309,5 +309,31 @@ namespace MathNet.Numerics
 
             throw new ArgumentException(Properties.Resources.ArgumentTooLargeForIterationLimit, "a,b");
         }
+
+        /// <summary>
+        /// Computes the logit function. <seealso cref="http://en.wikipedia.org/wiki/Logit"/>
+        /// </summary>
+        /// <param name="p">The parameter for which to compute the logit function. This number should be
+        /// between 0 and 1.</param>
+        /// <returns>The logarithm of <paramref name="p"/> divided by 1.0 - <paramref name="p"/>.</returns>
+        public static double Logit(double p)
+        {
+            if (p < 0.0 || p > 1.0)
+            {
+                throw new ArgumentOutOfRangeException(Resources.ArgumentBetween0And1);
+            }
+
+            return Math.Log(p / (1.0 - p));
+        }
+
+        /// <summary>
+        /// Computes the logistic function. <seealso cref="http://en.wikipedia.org/wiki/Logistic"/>
+        /// </summary>
+        /// <param name="p">The parameter for which to compute the logistic function.</param>
+        /// <returns>The logistic function of <paramref name="p"/>.</returns>
+        public static double Logistic(double p)
+        {
+            return 1.0 / (Math.Exp(-p) + 1.0);
+        }
     }
 }

src/UnitTests/SpecialFunctionsTests/SpecialFunctionsTests.cs

@@ -230,5 +230,35 @@ namespace MathNet.Numerics.UnitTests.SpecialFunctionsTests
         {
             AssertHelpers.AlmostEqual(f, SpecialFunctions.BetaRegularized(a,b,x), 12);
         }
+
+        [Test]
+        [Row(0.000000, Double.NegativeInfinity)]
+        [Row(0.000010, -11.512915464920228103874353849992239636376994324587)]
+        [Row(0.001000, -6.9067547786485535272274487616830597875179908939086)]
+        [Row(0.100000, -2.1972245773362193134015514347727700402304323440139)]
+        [Row(0.500000, 0.0)]
+        [Row(0.900000, 2.1972245773362195801634726294284168954491240598975)]
+        [Row(0.999000, 6.9067547786485526081487245019905638981131702804661)]
+        [Row(0.999990, 11.512915464924779098232747799811946290419057060965)]
+        [Row(1.000000, Double.PositiveInfinity)]
+        public void Logit(double p, double x)
+        {
+            AssertHelpers.AlmostEqual(x, SpecialFunctions.Logit(p), 15);
+        }
+
+        [Test]
+        [Row(0.000000, Double.NegativeInfinity)]
+        [Row(0.000010, -11.512915464920228103874353849992239636376994324587)]
+        [Row(0.001000, -6.9067547786485535272274487616830597875179908939086)]
+        [Row(0.100000, -2.1972245773362193134015514347727700402304323440139)]
+        [Row(0.500000, 0.0)]
+        [Row(0.900000, 2.1972245773362195801634726294284168954491240598975)]
+        [Row(0.999000, 6.9067547786485526081487245019905638981131702804661)]
+        [Row(0.999990, 11.512915464924779098232747799811946290419057060965)]
+        [Row(1.000000, Double.PositiveInfinity)]
+        public void Logistic(double x, double p)
+        {
+            AssertHelpers.AlmostEqual(x, SpecialFunctions.Logistic(p), 15);
+        }
     }
 }