MPI_Bcast Bcast stands for broadcast, and is used to send data from one process to all other processes. The format for this function is: MPI_Bcast(&msg_address,#_elements,MPI_Type, ID, Communicator). MPI_Bcast (&k, 1, MPI_INT, 0, MPI_COMM_WORLD) Process 0 sends k to all other processes

MPI_Bcast This function is best used when a some data that a process was using is changed, and it needs to get updated by all other processes in that communicator (ie: the next homework). Note: A call to MPI_Bcast must be placed where all processes can see it, if not the sending process will block and hang, waiting for an acknowledgement.

MPI_Bcast Process 1 Data written, unblock Data Present Data Empty Write data to all processes Process 2 Process 3 Process 0 Data Present

Simple Program that Demonstrates MPI_Bcast: #include <mpi.h> #include <stdio.h> int main (int argc, char *argv[]){ int k,id,p,size; MPI_Init(&argc,&argv); MPI_Comm_rank(MPI_COMM_WORLD, &id); MPI_Comm_size(MPI_COMM_WORLD, &size); if(id == 0) k = 20; else k = 10; for(p=0; p<size; p++){ if(id == p) printf("Process %d: k= %d before\n",id,k); } //note MPI_Bcast must be put where all other processes //can see it. MPI_Bcast(&k,1,MPI_INT,0,MPI_COMM_WORLD); printf("Process %d: k= %d after\n",id,k); MPI_Finalize(); return 0

The Output would look like: Process 0: k= 20 before Process 0: k= 20 after Process 3: k= 10 before Process 3: k= 20 after Process 2: k= 10 before Process 2: k= 20 after Process 1: k= 10 before Process 1: k= 20 after