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Cosine.cs
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Cosine.cs
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// Accord Math Library
// The Accord.NET Framework
// http://accord-framework.net
//
// Copyright © César Souza, 2009-2017
// cesarsouza at gmail.com
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
//
namespace Accord.Math.Distances
{
using System;
using System.Runtime.CompilerServices;
using Accord.Compat;
/// <summary>
/// Cosine distance. For a proper distance metric, see <see cref="Angular"/>.
/// </summary>
///
/// <seealso cref="Angular"/>
///
/// <example>
/// <code source="Unit Tests\Accord.Tests.Math\DistanceTest.cs" region="doc_cosine_2" />
/// </example>
///
[Serializable]
public struct Cosine : IDistance<double[]>, ISimilarity<double[]>
{
/// <summary>
/// Computes the distance <c>d(x,y)</c> between points
/// <paramref name="x"/> and <paramref name="y"/>.
/// </summary>
///
/// <param name="x">The first point <c>x</c>.</param>
/// <param name="y">The second point <c>y</c>.</param>
///
/// <returns>
/// A double-precision value representing the distance <c>d(x,y)</c>
/// between <paramref name="x"/> and <paramref name="y"/> according
/// to the distance function implemented by this class.
/// </returns>
///
/// <example>
/// <code source="Unit Tests\Accord.Tests.Math\DistanceTest.cs" region="doc_cosine_2" />
/// </example>
///
#if NET45 || NET46 || NET462 || NETSTANDARD2_0
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public double Distance(double[] x, double[] y)
{
double sum = 0;
double p = 0;
double q = 0;
for (int i = 0; i < x.Length; i++)
{
sum += x[i] * y[i];
p += x[i] * x[i];
q += y[i] * y[i];
}
double den = Math.Sqrt(p) * Math.Sqrt(q);
return sum == 0 ? 1.0 : 1.0 - (sum / den);
}
/// <summary>
/// Gets a similarity measure between two points.
/// </summary>
///
/// <param name="x">The first point to be compared.</param>
/// <param name="y">The second point to be compared.</param>
///
/// <returns>A similarity measure between x and y.</returns>
///
#if NET45 || NET46 || NET462 || NETSTANDARD2_0
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public double Similarity(double[] x, double[] y)
{
double sum = 0;
double p = 0;
double q = 0;
for (int i = 0; i < x.Length; i++)
{
sum += x[i] * y[i];
p += x[i] * x[i];
q += y[i] * y[i];
}
double den = Math.Sqrt(p) * Math.Sqrt(q);
return (sum == 0) ? 0 : sum / den;
}
}
}