d11r4.cpp

Visual C++ 常用数值算法集 源代码

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

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

double deriv(double x)
{
    return -bessj1(x);
}

void main()
{
	//program d11r4
    //driver for routine dbrent
    double dbr,ax,bx,cx,fa,fb,fc,tol = 0.000001;
    double xmin;
	double 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)   dbrent"<<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);
        dbr = dbrent(ax, bx, cx, tol, xmin);
        if (nmin == 0)
		{
            amin[1] = xmin;
            nmin = 1;
			cout<<"  "<<nmin<<"      ";
			cout.width(14);       cout<<xmin;
			cout.width(14);       cout<<bessj0(xmin);
			cout.width(14);       cout<<deriv(xmin);
			cout.width(14);	   cout<<dbr;
			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(14);	 cout<<xmin;
				cout.width(14);	 cout<<bessj0(xmin);
				cout.width(14);	 cout<<deriv(xmin);
				cout.width(14);	 cout<<dbr;
				cout<<endl;
            }
        }
    }
}