d3r7.cpp

这个是常用的数值算法用VC编写的。相信对大家有用哦。

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

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

void qgaus(double a, double b, double& ss)
{
	double xm,xr,dx;
    double x[6], w[6];
    x[1] = 0.1488743389;
    x[2] = 0.4333953941;
    x[3] = 0.6794095682;
    x[4] = 0.8650633666;
    x[5] = 0.9739065285;
    w[1] = 0.2955242247;
    w[2] = 0.2692667193;
    w[3] = 0.2190863625;
    w[4] = 0.1494513491;
    w[5] = 0.0666713443;
    xm = 0.5 * (a + b);
    xr = 0.5 * (b - a);
    ss = 0.0;
    for (int j = 1; j<=5; j++)
	{
        dx = xr * x[j];
        ss = ss + w[j] * (func(xm + dx) + func(xm - dx));
    }
    ss = xr * ss;
}

void main()
{
    //program d3r7
    //driver for routine qgaus
    double x,ss,aaa,dx, x1 = 0.0;
    double x2 = 5.0;
    int nval = 10;
    dx = (x2 - x1) /(double)nval;
    cout<<endl;
    cout<<"    0.0to          qgaus        expected"<<endl;
	cout.setf(ios::fixed|ios::right);
	for (int i = 1; i<=nval; i++)
	{
        x = x1 + (double)i * dx;
        qgaus(x1, x, ss);
        cout<<"    "<<x;
		cout.precision(6);
		cout.width(14);
        cout<<ss;
        aaa = -(1.0 + x) * exp(-x) + (1.0 + x1) * exp(-x1);
		cout.width(14);
        cout<<aaa<<endl;
    }
}