mathnet-numerics/src/Managed/SpecialFunctions.cs

// <copyright file="SpecialFunctions.cs" company="Math.NET">
// Math.NET Numerics, part of the Math.NET Project
// http://mathnet.opensourcedotnet.info
//
// Copyright (c) 2009 Math.NET
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using System;

namespace MathNet.Numerics
{
    /// <summary>
    /// This class implements a collection of special function evaluations for double precision. This class 
    /// has a static constructor which will precompute a small number of values for faster runtime computations.
    /// </summary>
    public static partial class SpecialFunctions
    {
        /// <summary>
        /// Computes the hypotenuse of a right angle triangle.
        /// </summary>
        /// <param name="a">The length of side a of the triangle.</param>
        /// <param name="b">The length of side b of the triangle.</param>
        /// <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 (Math.Abs(a) > Math.Abs(b))
            {
                double r = b / a;
                return Math.Abs(a) * Math.Sqrt(1 + r * r);
            }

            if (b.AlmostZero())
            {
                double r = a / b;
                return Math.Abs(b) * Math.Sqrt(1 + r * r);
            }

            return 0d;
        }
    }
}