#include "iostream.h"
#include "math.h"

double func(double x)
{
    return x * exp(-x);
}

void main()
{
    //program d3r8
    //driver for routine gauleg
    int i,npoint = 10;
    double x1 = 0.0;
    double x2 = 1.0;
    double x3 = 10.0;
    double x[11], w[11];
    gauleg(x1, x2, x, w, npoint);
    cout<<endl;
    cout<<"      #       x(i)        w(i)"<<endl;
	cout.setf(ios::fixed|ios::right);
	cout.precision(6);
    for (i = 1; i<=npoint; i++)
	{
		cout.width(2);
        cout<<"      "<<i;
		cout.width(12);
        cout<<x[i];
		cout.width(12);
        cout<<w[i]<<endl;
    }
    //demonstrate the use of gauleg for an integral
    gauleg(x1, x3, x, w, npoint);
    double xx = 0.0;
    for (i = 1; i<=npoint; i++)
	{
        xx = xx + w[i] * func(x[i]);
    }
    cout<<endl;
    cout<<"integral from gauleg:  "<<xx<<endl;
    cout<<"actual value:  ";
    cout<<(1.0 - (1.0 + x3) * exp(-x3))<<endl;
}