MPI 加农算法
加农算法计算矩阵相乘 为了实现方便 只实现了矩阵自乘 而且 实际上各线程都可读取整个矩阵（略去输入和分配中的通信过程）
在各线程相互交换数据的过程中 一定要注意避免死锁
#include "mpi.h"#include <stdio.h>#include <stdlib.h>#include <math.h>#define TAG 0static inline void rtoij(int r,int w,int *i,int *j) {//rank to i,j*i=r/w;*j=r-(*i)*w;}static inline void ijtor(int i,int j,int *r,int w) {//i,j to rank*r=i*w+j;}static inline int aj(int i,int j,int w) {return (j+i)%w;}static inline int bi(int i,int j,int w) {//initial b distributereturn aj(i,j,w);}int main(int argc,char *argv[]) {float m[][2]={{1,2}, {3,4}};//the matrix //multiply by itselfint self,size;MPI_Init(&argc,&argv);MPI_Comm_rank(MPI_COMM_WORLD,&self);MPI_Comm_size(MPI_COMM_WORLD,&size);MPI_Request r;MPI_Status s;int w=sqrt(size);int i,j,an,bn,ap,bp;rtoij(self,w,&i,&j);ijtor(i,(j+w-1)%w,&an,w);//next a processijtor((i+w-1)%w,j,&bn,w);//next b processijtor(i,(j+1)%w,&ap,w);//previous a processijtor((i+1)%w,j,&bp,w);float res,a,b,tmp;//initialize data distributiona=m[i][aj(i,j,w)];b=m[bi(i,j,w)][j];res=a*b;for(int i=0;i<w-1;++i) {MPI_Issend(&a,1,MPI_FLOAT,an,TAG,MPI_COMM_WORLD,&r);//avoid dead lockMPI_Recv(&tmp,1,MPI_FLOAT,ap,TAG,MPI_COMM_WORLD,&s);a=tmp;MPI_Wait(&r,&s);MPI_Issend(&b,1,MPI_FLOAT,bn,TAG,MPI_COMM_WORLD,&r);//avoid dead lockMPI_Recv(&tmp,1,MPI_FLOAT,bp,TAG,MPI_COMM_WORLD,&s);b=tmp;MPI_Wait(&r,&s);res+=a*b;}if(0==self) {printf("%f",res);for(int i=1;i<size;++i) {MPI_Recv(&res,1,MPI_FLOAT,i,TAG,MPI_COMM_WORLD,&s);printf(" %f",res);}printf("\n");} else {MPI_Ssend(&res,1,MPI_FLOAT,0,TAG,MPI_COMM_WORLD);}MPI_Finalize();return 0;}