並行計算多線程冪級數計算pi

使用多線程，冪級數方法來計算pi，方法如下。

這樣就很簡單了，只要把握好線程函數的計算範圍即可了。
完整程序如下

//
//  main.cpp
//  pi
//
//  Created by Yuuki on 2020/4/29.
//  Copyright © 2020 Yuuki. All rights reserved.
//

#include <iostream>
#include <pthread.h>
#include <iomanip>
#include <ctime>
using namespace std;

double pi = 0.0;
int N,T;
pthread_mutex_t mut;
//線程入口函數
void *thread_function(void *arg){
    //int *income = (int *)arg;
    int id = *(int *)arg;
    int piece = N/T;
    int start = id*piece;
    int end = start + piece;
    double local_pi = 0.0;
    double factor;
    if(start%2 == 0)
        factor = 1.0;
    else
        factor = -1.0;
    for(int i=start;i<end;i++,factor = -factor){
        local_pi += factor/(2*i+1);
    }
    pthread_mutex_lock(&mut);
    pi += 4.0*local_pi;
    pthread_mutex_unlock(&mut);

    return NULL;
}

int main(int argc, const char * argv[]) {
    cout<<"並行積分法求兀的值,輸入級數和線程數"<<endl;
    cin>>N>>T;
    pthread_t thread[T];
    int x[T];
    for(int i=0;i<T;i++){
        x[i] = i;
        pthread_create(&thread[i], NULL, thread_function, &x[i]);
    }
    for(int i=0;i<T;i++){
        pthread_join(thread[i], NULL);
    }   
    return 0;
}