Beispiel #1
0
    public static double p20_exact(ref p20Data data)

    //****************************************************************************80
    //
    //  Purpose:
    //
    //    P20_EXACT returns the exact integral for problem 20.
    //
    //  Licensing:
    //
    //    This code is distributed under the GNU LGPL license.
    //
    //  Modified:
    //
    //    27 December 2011
    //
    //  Author:
    //
    //    John Burkardt
    //
    //  Parameters:
    //
    //    Output, double P20_EXACT, the value of the integral.
    //
    {
        double exact = (
            Math.Log(1.5) / Math.Pow(2.0, p20Data.beta)
            - 1.0 / Math.Pow(2.0, p20Data.beta + 1.0) *
            Math.Log((16.0 + Math.Pow(0.25, p20Data.beta)) / (1.0 + Math.Pow(0.25, p20Data.beta)))
            - Math.Atan(Math.Pow(2.0, p20Data.beta + 2.0)) - Math.Atan(Math.Pow(2.0, p20Data.beta))
            ) / (1.0 + Math.Pow(0.25, p20Data.beta));

        return(exact);
    }
Beispiel #2
0
    public static double[] p20_fun(ref p20Data data, int n, double[] x)

    //****************************************************************************80
    //
    //  Purpose:
    //
    //    P20_FUN evaluates the integrand for problem 20.
    //
    //  Integral:
    //
    //    Integral ( 0 <= x < +oo )
    //      1 / ( 2^beta * ( ( x - 1 )^2 + (1/4)^beta ) * ( x - 2 ) ) dx
    //
    //  Licensing:
    //
    //    This code is distributed under the GNU LGPL license.
    //
    //  Modified:
    //
    //    27 December 2011
    //
    //  Author:
    //
    //    John Burkardt
    //
    //  Reference:
    //
    //    Robert Piessens, Elise de Doncker-Kapenga,
    //    Christian Ueberhuber, David Kahaner,
    //    QUADPACK: A Subroutine Package for Automatic Integration,
    //    Springer, 1983, page 84.
    //
    //  Parameters:
    //
    //    Input, int N, the number of evaluation points.
    //
    //    Input, double X[N], the evaluation points.
    //
    //    Output, double P20_FUN[N], the integrand values.
    //
    {
        int i;

        double[] fx = new double[n];

        for (i = 0; i < n; i++)
        {
            if (Math.Pow(x[i] - 1.0, 2) + Math.Pow(0.25, p20Data.beta) == 0.0 || Math.Abs(x[i] - 2.0) <= double.Epsilon)
            {
                fx[i] = 0.0;
            }
            else
            {
                fx[i] = 1.0 /
                        (Math.Pow(2.0, p20Data.beta)
                         * (Math.Pow(x[i] - 1.0, 2) + Math.Pow(0.25, p20Data.beta))
                         * (x[i] - 2.0));
            }
        }

        return(fx);
    }