// <copyright file="Logistic.cs" company="Math.NET">
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// Math.NET Numerics, part of the Math.NET Project
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// http://numerics.mathdotnet.com
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// http://github.com/mathnet/mathnet-numerics
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//
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// Copyright (c) 2009-2011 Math.NET
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//
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// Permission is hereby granted, free of charge, to any person
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// obtaining a copy of this software and associated documentation
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// files (the "Software"), to deal in the Software without
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// restriction, including without limitation the rights to use,
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// copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the
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// Software is furnished to do so, subject to the following
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// conditions:
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//
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// The above copyright notice and this permission notice shall be
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// included in all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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// OTHER DEALINGS IN THE SOFTWARE.
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// </copyright>
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// <contribution>
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// Cephes Math Library, Stephen L. Moshier
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// ALGLIB 2.0.1, Sergey Bochkanov
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// </contribution>
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using System;
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// ReSharper disable CheckNamespace
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namespace IStation.Numerics
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// ReSharper restore CheckNamespace
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{
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/// <summary>
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/// This partial implementation of the SpecialFunctions class contains all methods related to the logistic function.
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/// </summary>
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public static partial class SpecialFunctions
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{
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/// <summary>
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/// Computes the logistic function. see: http://en.wikipedia.org/wiki/Logistic
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/// </summary>
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/// <param name="p">The parameter for which to compute the logistic function.</param>
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/// <returns>The logistic function of <paramref name="p"/>.</returns>
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public static double Logistic(double p)
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{
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return 1.0/(Math.Exp(-p) + 1.0);
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}
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/// <summary>
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/// Computes the logit function, the inverse of the sigmoid logistic function. see: http://en.wikipedia.org/wiki/Logit
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/// </summary>
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/// <param name="p">The parameter for which to compute the logit function. This number should be
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/// between 0 and 1.</param>
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/// <returns>The logarithm of <paramref name="p"/> divided by 1.0 - <paramref name="p"/>.</returns>
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public static double Logit(double p)
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{
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if (p < 0.0 || p > 1.0)
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{
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throw new ArgumentOutOfRangeException(nameof(p), "The argument must be between 0 and 1.");
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}
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return Math.Log(p/(1.0 - p));
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}
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}
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}
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