程序並行化使用OpenMP C++

Question

我試圖計算積分

#include <iostream> 
#include <omp.h> 

using namespace std; 

double my_exp(double x) { 
    double res = 1., term = 1.; 
    for(int n=1; n<=1000; n++) { 
    term *= x/n; 
    res += term; 
    } 
    return res; 
} 

double f(double x) { 
    return x*my_exp(x); 
} 


int main() { 
    double a=0., b=1., result = 0.; 
    int nsteps = 1000000; 
    double h = (b - a)/nsteps; 


    for(int i=1; i<nsteps; i++) result += f(a + i*h); 
    result = (result + .5*(f(a) + f(b)))*h; 

    cout.precision(15); 
    cout << "Result: " << result << endl; 
    return 0; 
} 

這項計劃數積分和返回結果Result: 1.00000000000035 來算積分。但執行時間很多。 我應該平行我的計劃，我想我應該補充#pragma omp parallel for，但它不工作

Answer 1

改變你的主要功能

#pragma omp parallel 
    { 
    double localresult = 0.0; 
#pragma omp for 
    for(int i=1; i<nsteps; i++) 
     localresult += f(a + i*h); 
#pragma omp critical 
    { 
     result += localresult; 
    } 
    } 

    result = (result + .5*(f(a) + f(b)))*h; 

編輯：沿muXXmit2X的線條更簡單的解決辦法是

#pragma omp parallel for reduction(+:result) 
for(int i=1; i<nsteps; i++) result += f(a + i*h); 

result = (result + .5*(f(a) + f(b)))*h;