怎麼樣用用MPI編寫兩個n階的方陣A和B的相乘程序,結果存放在方陣C中,A、B和C都在節點0中呢?
//#include<stdio.h>
//#include<math.h>
//#pragma comment(lib,"mpi.lib")
#include<mpi.h>
#include<stdio.h>
#include <iostream>
#include<math.h>
#pragma comment(lib,"mpi.lib")
#define n 1000
using namespace std;
int main(int argv, char *argc[])
{
int rank, p, a;
MPI_Init(&argv, &argc);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &p);
MPI_Status status;
if (p!=1)
a = n / (p - 1);
if (rank == 0)
{
int* A = new int[n*n];
int* B = new int[n*n];
int* C = new int[n*n];
// int * recptr = NULL;
for (int i = 0; i < n; i++)
for (int j = 0; j < n; j++)// 時間是 O nn
{
A[i*n + j] = i + j; //A[i][j]
B[i*n + j] = 1; //B[i][j]
}
if (p == 1)
{
double tb, te;
tb = MPI_Wtime();
for (int i = 0; i < n; i++)
for (int j = 0; j < n; j++)
{
C[i*n + j] = 0; //C[i][j]
for (int k = 0; k < n; k++)
{
C[i*n + j] = A[i*n + k] * B[k*n + j];
}
}
te = MPI_Wtime();
cout << "time is " << te - tb;// << "s" << endl;
}
if (p != 1)
{
double tb, te;
tb = MPI_Wtime();
for (int i = 0; i < p-1; i++){//給每個寄存器發送 數組 A,B,C
MPI_Send(&A[0+0], n*n, MPI_INT, i+1, 1, MPI_COMM_WORLD);//每個發送 a行,a*n大小的數據
MPI_Send(&B[0+0], n*n, MPI_INT, i+1,2, MPI_COMM_WORLD);
}
for (int i =0; i < p-1; i++)
MPI_Recv(&C[i*a+0], a*n, MPI_INT, i+1,3, MPI_COMM_WORLD, &status);//每個接受 a行,a*n大小的數據
te = MPI_Wtime();
cout << "time is " << te - tb;// << "s" << endl;
}
delete[] A;
delete[] B;
delete[] C;
}
if (p != 1)
if (rank != 0){
int* A = new int[n*n];
int* B = new int[n*n];
int* C = new int[n*n];
MPI_Recv(&A[0+0], n*n, MPI_INT, 0, 1, MPI_COMM_WORLD, &status);//從A[0][0]和B[0][0]開始接受
MPI_Recv(&B[0+0], n*n, MPI_INT,0, 2, MPI_COMM_WORLD, &status);
for (int i =a*(rank-1); i < (a*(rank)); i++)//按照行間隔分,每個cpu計算自己的a行
for (int j = 0; j < n; j++)
{
C[i*n + j] = 0; //C[i][j]
for (int k = 0; k < n; k++)
{
C[i*n + j] = A[i*n + k] * B[k*n + j];
}
}
{//向rank=0發送自己的那a行C,大小是a*n
//int * sendptr = &(C[a*(rank - 1)+0]);
MPI_Send(&C[a*(rank - 1) + 0], a*n, MPI_INT, 0,3, MPI_COMM_WORLD);//起始地址是C[rank-1][0],大小是a*n
}
}
MPI_Finalize();
return 0;
}
經過測試,不同節點數的加速比如下:
兩個節點之所以沒有變化是因爲,一個負責發送數據,一個負責計算數據,還要發送回來,實際上和一個計算是沒什麼差別的。但是隨着節點數的增加,時間下降的速度呈指數小於0的指數函數下降趨勢,加速比呈k=0.27的一次方程上漲,從與上一個節點的加速比例比較來看,可見每增加一倍節點的數量,只能提高1.2的速度。