谁有关于定积分的算法阿，谢谢，急用

Question

谁有关于定积分的算法阿，谢谢，急用

Answer 1

#include <iostream.h>
#include <iomanip.h>
#include<math.h>double f(double x);void main(){   
     int n=1;  //初值
     double a=0,b=1;
     double  h,Tn,T2n,In,I2n;
     
     const double eps=1e-8;
    
     h=b-a;
     T2n=I2n=h*(f(a)+f(b))/2;
     In=0;     while(fabs(I2n-In)>=eps)  //求积分
     {
         Tn=T2n;
         In=I2n;
         
         double sigma=0.0;
         for(int k=0;k<n; K++)  //求变步长梯形的和部分
         {
            double x=a+(K+0.5)*h;
            sigma+=f(x);
         }
       
         T2n=(Tn+h*sigma)/2.0; //变步长梯形
         I2n=(4*T2n-Tn)/3.0    //辛普生公式         n*=2;                //划分
         h/=2;
     } 
       
     cout<<"the integral of f(x) from" <<a<<"to" <<b<<"is \n"
                                       <<setiosflags(ios::fixed)
                                       <<setprecision(8)
                                       <<setw(10)<<I2n<<endl; //输出结果
}     double f(double x)
     {
          return   exp(x)/(1+x*x);
     }

Answer 2

#include <iostream.h>
#include <iomanip.h>
#include<math.h>double f(double x);void main(){   
     int n=1;  //初值
     double a=0,b=1;
     double  h,Tn,T2n,In,I2n;
     
     const double eps=1e-8;
    
     h=b-a;
     T2n=I2n=h*(f(a)+f(b))/2;
     In=0;     while(fabs(I2n-In)>=eps)  //求积分
     {
         Tn=T2n;
         In=I2n;
         
         double sigma=0.0;
         for(int k=0;k<n; K++)  //求变步长梯形的和部分
         {
            double x=a+(K+0.5)*h;
            sigma+=f(x);
         }
       
         T2n=(Tn+h*sigma)/2.0; //变步长梯形
         I2n=(4*T2n-Tn)/3.0    //辛普生公式         n*=2;                //划分
         h/=2;
     } 
       
     cout<<"the integral of f(x) from" <<a<<"to" <<b<<"is \n"
                                       <<setiosflags(ios::fixed)
                                       <<setprecision(8)
                                       <<setw(10)<<I2n<<endl; //输出结果
}     double f(double x)
     {
          return   exp(x)/(1+x*x);
     }