Fundamentals - Parallel Processing - Lecture Slides, Slides of Parallel Computing and Programming

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MPI Fundamentals—A Quick

Overview

Intro by Example

Blocking Send’s and Receive’s

Blocking Send’s and Receive’s (contd.)

Blocking Send’s and Receive’s (contd.)

Blocking Send’s and Receive’s (contd.)

An example: MPI_Status status; MPI_Recv( ..., &status ); ... status.MPI_TAG; ... status.MPI_SOURCE; MPI_Get_count( &status, datatype, &count ); MPI_TAG and MPI_SOURCE primarily of use when MPI_ANY_TAG and/or MPI_ANY_SOURCE in the receive. MPI_Get_count may be used to determine how much data of a particular type was received.

Blocking Send’s and Receive’s (contd.)

Blocking Send’s and Receive’s (contd.)

Blocking Send’s and Receive’s (contd.)

Blocking Send’s and Receive’s (contd.)

Collective operations: An Example

#include "mpi.h“

#include <math.h>

int main(argc,argv)

int argc; char *argv[];

int done = 0, n, myid, numprocs, i, rc;

double PI25DT = 3.141592653589793238462643;

double mypi, pi, h, sum, x, a;

MPI_Init(&argc,&argv);

MPI_Comm_size(MPI_COMM_WORLD,&numprocs); MPI_Comm_rank(MPI_COMM_WORLD,&myid);

while (!done)

{ if (myid == 0) { printf("Enter the number of intervals: (0 quits) "); scanf("%d",&n); }

MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);

if (n == 0) break;

h = 1.0 / (double) n; sum = 0.0;

for (i = myid + 1; i <= n; i += numprocs)

x = h * ((double)i - 0.5); sum += 4.0 / (1.0 + x*x);

mypi = h * sum;

MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);

if (myid == 0) printf("pi is approximately %.16f, Error is %.16f\n", pi, fabs(pi - PI25DT));

MPI_Finalize();

Run either program for PI. Write new versions that replace the calls to MPI_Bcast and MPI_Reduce with

MPI_Send and MPI_Recv.