d2r3.cpp

来自「visual c++查过能用数值算法 附带光盘里面的源代码」· C++ 代码 · 共 36 行

# include<iostream.h>
# include<math.h>
# include<iomanip.h>

void main()
{
	double x[21], y[21], y2[21],pi,yp1,ypn ;
	int n, i;
    //program d2r3
    //driver for routine spline
    n = 20;
    pi = 3.1415926;
    //生成插值数组
    for (i = 1;i<=20;i++)
	{
        x[i] = i * pi / n;
        y[i] = sin(x[i]);
    }
    //用三次样条函数计算二阶导数
    yp1 = cos(x[1]);
    ypn = cos(x[n]);
    cout<<endl;   
    cout<<"Second-derivative for sin(x) from 0 to pi"<<endl;
    spline(x, y, n, yp1, ypn, y2);
    //验证计算结果
    cout<<"                     spline        actual"<<endl;
    cout<<"        angle      2nd deriv     2nd deriv"<<endl;
    for( i = 1;i<=n;i++)
	{
		cout<<setprecision(6)<<setiosflags(ios::fixed);
        cout<<setw(14)<<x[i];
        cout<<setw(14)<<y2[i];
        cout<<setw(14)<<-sin(x[i])<<endl;
    } 
}