trapz.txt

梯形算法

//Trapz.h
#include <iostream>
#include <cmath>
using namespace std;
class F
{
   public:
      virtual double operator ()(double x) const=0;
};

class Fun:public F
{
   public:
      double operator ()(double x) const
          {
               return log(1.0+x)/(1.0+x*x);
          }
};

class Integ
{
    public:
       virtual double operator ()(double a,double b,double eps) const=0;
};

class Trapz:public Integ
{
    public:
        Trapz(class F &pf):f(pf)  {}
        double operator ()(double a,double b,double eps) const;
    private:
        class F &f;
};
//end


//Trapz.cpp
#include "Trapz.h"
double Trapz::operator ()(double a,double b,double eps) const
{
    double Tn,T2n,temp,h,xk;
    int k,n=1,done=0;
    h=b-a;
    
    //赋初值
    Tn=(f(a)+f(b))*h/2.0;

    while(!done)
     {
       temp=0.0;  
       for(k=0;k<n;k++)
	   {
		   xk=a+(k+0.5)*h;
	       temp+=f(xk);
	   }
       T2n=(Tn+h*temp)/2.0;
       if(T2n-Tn<eps)
           done=1;
       else
         {
            Tn=T2n;
            n=n*2;
            h=h/2;
         }
      }
          return T2n;
}

//Main.cpp
#include "Trapz.h"
#include <iomanip>
void main()
{
   Fun f;
   Trapz trapz(f);
   cout<<"TRAPZ Int:"<<setprecision(7)<<trapz(0,2,1e-7)
       <<endl;
}