Example 3: Integral of the entire real line

using System;
using Imsl.Math;

public class QuadratureEx3 : Quadrature.IFunction
{
    public double F(double x)
    {
        return x / (4.0 * Math.Exp(x) + 9.0 * Math.Exp(-x));
    }


    public static void  Main(String[] args)
    {        
        Quadrature q = new Quadrature();
        Quadrature.IFunction fcn = new QuadratureEx3();
        double result = q.Eval(fcn, Double.NegativeInfinity, 
            Double.PositiveInfinity);
        
        double expect = System.Math.PI * System.Math.Log(1.5) / 12.0;
        Console.Out.WriteLine("result = " + result);
        Console.Out.WriteLine("expect = " + expect);
    }
}

Output

result = 0.106150517076628
expect = 0.106150517076633

Reference