my.c

利用MPI_SEND 和mpi_recv来模拟mpi_Bcast和mpi_reduce.

#include <stdlib.h>
#include <stdio.h>
#include <mpi.h>

const int dimension = 20000;

void generateNumbers(int seed, double *A)
{
  int i, j;

  srand(100*seed);
  for(i = 0; i < dimension; i++)
    for(j = 0; j < dimension; j++)
      A[dimension*i+j] = (rand()/(RAND_MAX + 1.0));
}

void maxMatrix(double *A, double *Amax)
{
  int i, j;

  for(i = 0; i < dimension; i++)
  {
    Amax[i] = -1.0;
    for(j = 0; j < dimension; j++)
      if(A[dimension*i+j] > Amax[i])
	Amax[i] = A[dimension*i+j];
  }
}

double maxVector(double *A)
{
  int i;
  double Amax = -1.0;

  for(i = 0; i < dimension; i++)
    if(A[i] > Amax)
	Amax = A[i];

  return Amax;
}

int main(int argc, char **argv)
{
  int rank, size;
  int i;
  double *A, *Amax, *rootMax;
  double tick, tock, maxVal = -1.0;
  MPI_Status status;  

  A = (double*)malloc(dimension*dimension*sizeof(double));
  Amax = (double*)malloc(dimension*sizeof(double));
  rootMax = (double*)malloc(dimension*sizeof(double));

  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);

  generateNumbers(rank, A);

  tick = MPI_Wtime();
  maxMatrix(A, Amax);
  tock = MPI_Wtime();

  printf("Processor %d, find local max took %f sec\n", rank, tock-tick);
  
  tick = MPI_Wtime();
	
  if (rank != 0)
        {
                 MPI_Send(Amax, dimension, MPI_DOUBLE, 0, rank, MPI_COMM_WORLD);

        }
   else
        {
		 memcpy(A, Amax, dimension); 
		 for (i=1;i<size;i++)
			{
                		MPI_Recv(Amax,dimension,MPI_DOUBLE,i,i,MPI_COMM_WORLD,&status);
				memcpy(&A[i*dimension],Amax,dimension);
			}
		maxMatrix(A, rootMax);
        }

//  MPI_Reduce(Amax, rootMax, dimension, MPI_DOUBLE, MPI_MAX, 0, MPI_COMM_WORLD);

  tock = MPI_Wtime();

  if(rank == 0)
  {
    printf("The modified reducsion with send  took: %f sec\n", tock-tick);
    tick = MPI_Wtime();
    maxVal = maxVector(rootMax);
    tock = MPI_Wtime();
    printf("find max took %f sec\n", tock-tick);
  }

  tick = MPI_Wtime();

  if (rank == 0)
	{
		for (i=1;i<size;i++) 
			MPI_Send(&maxVal, 1, MPI_DOUBLE, i, i, MPI_COMM_WORLD);

	}
   else
	{
		MPI_Recv(&maxVal,1,MPI_DOUBLE,0,rank,MPI_COMM_WORLD,&status); 
	}
//  MPI_Bcast(&maxVal, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);

  tock = MPI_Wtime();


  if(rank == 0)
    printf("the modified broadcast with send  took: %f sec\n", tock-tick);

  printf("Processor %d, max %f\n", rank, maxVal);

  MPI_Finalize();

  return EXIT_SUCCESS;
}