并行计算多线程幂级数计算pi

使用多线程，幂级数方法来计算pi，方法如下。

这样就很简单了，只要把握好线程函数的计算范围即可了。
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;
//线程入口函数
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;elsefactor = -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<<"并行积分法求兀的值,输入级数和线程数"<<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;
}