d11r3.cpp

来自「工程算法 这是一个很有用的工程数值算法集锦」· C++ 代码 · 共 62 行

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

double func(double x)
{
    return bessj0(x);
}

void main()
{
    //program d11r3
    //driver for routine brent
    double b,ax,bx,cx,fa,fb,fc,tol = 0.000001;
    double xmin,eql = 0.0001;
    double amin[21];
    int iflag,i,nmin = 0;
    cout<<endl;
    cout<<"minima of the function Bessj0"<<endl;
    cout<<endl;
    cout<<"min.#     x      Bessj0(x)     Bessj1(x)"<<endl;
	cout.setf(ios::fixed|ios::left);
	cout.precision(6);
    for (i = 1; i<=100; i++)
	{
        ax = i;
        bx = i + 1.0;
        mnbrak(ax, bx, cx, fa, fb, fc);
        b = brent(ax, bx, cx, tol, xmin);
        if (nmin == 0)
		{
            amin[1] = xmin;
            nmin = 1;
			cout<<"  "<<nmin<<"    ";
			cout.width(16);       cout<<xmin;
			cout.width(16);       cout<<bessj0(xmin);
			cout.width(16);       cout<<bessj1(xmin);
			cout<<endl;
		}
        else
		{
            iflag = 0;
            for (int j = 1; j<=nmin; j++)
			{
                if (fabs(xmin - amin[j]) <= eql * xmin)
				{
					iflag = 1;
				}
            }
            if (iflag == 0)
			{
                nmin = nmin + 1;
                amin[nmin] = xmin;
				cout<<"  "<<nmin<<"    ";
				cout.width(16);	 cout<<xmin;
				cout.width(16);	 cout<<bessj0(xmin);
				cout.width(16);	 cout<<bessj1(xmin);
				cout<<endl;
            }
        }
	}
}