任意积分求法

Posted 2021-03-03 ls-pankong

#include<iostream>
#include<cmath>
using namespace std;
typedef double (*fpoint)(double x);　　//新定义的函数类型，里边有一个double变量
double fun1(double x){
    const int u=0;
    const int b=1;
    const double Pi=3.14159;
    double coefficient=1/(sqrt(2*Pi)*b);
    double index = -((x-u)*(x-u)/(2*b*b));
    return coefficient*exp(index); 
}
double fun2(double x){
    return 3*x*x+4*x;
}
double fun3(double x){
    return exp(x);
}
double fintegration(fpoint f,const long long N=50000,const double minvalue=-1000,const double maxvalue=1000){
    double distance=(maxvalue-minvalue)/N;
    long double sum=0;
    for(int i=0;i<N;i++){
        double length;
        double x1,x2;
        x1=minvalue+i*distance;
        x2=minvalue+(i+1)*distance;
        length=(f(x1)+f(x2))/2;
        sum+=length*distance;
    }
    return sum;
}
int main(){
    int m,n;
    double q;
    cout<<"请输入积分区间: ";
    cin>>m>>n;
    cout<<"请输入精度:";
    cin>>q;
    double w = (n-m)/q;
    cout<<w<<endl;
    cout<<fintegration(fun3,w,m,n)<<endl;
    return 0;
}