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PP Lab

PP Lab. MPI programming VI. Program 1. Write a parallel program that calculates the sum of all numbers in a vector. Calculate the partial sums . Add the partial sums for the final answer. Functions to be used. MPI_Scatter: Sends data from one task to all other tasks in a group. Synopsis:

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PP Lab

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  1. PP Lab MPI programming VI

  2. Program 1 Write a parallel program that calculates the sum of all numbers in a vector. • Calculate the partial sums. • Add the partial sums for the final answer.

  3. Functions to be used • MPI_Scatter: Sends data from one task to all other tasks in a group. • Synopsis: #include "mpi.h" int MPI_Scatter ( void *sendbuf, int sendcnt, MPI_Datatype sendtype, void *recvbuf, int recvcnt, MPI_Datatype recvtype, int root, MPI_Comm comm ) • Input Parameters: • sendbuf: address of send buffer • sendcount: number of elements sent to each process • sendtype: data type of send buffer elements the above three arguments are significant only at root. • recvcount: number of elements in receive buffer • recvtype: data type of receive buffer elements • root: rank of sending process • comm: communicator • Output Parameter: • recvbuf: address of receive buffer

  4. Functions to be used • MPI_Gather: Gathers together values from a group of processes. • Synopsis: #include "mpi.h" int MPI_Gather ( void *sendbuf, int sendcnt, MPI_Datatype sendtype, void *recvbuf, int recvcount, MPI_Datatype recvtype, int root, MPI_Comm comm ) • Input Parameters: • sendbuf: starting address of send buffer • sendcount: number of elements in send buffer • sendtype: data type of send buffer elements • recvcount: number of elements for any single receive (significant only at root) • recvtype: data type of recv buffer elements (significant only at root) • root: rank of receiving process • comm: communicator • Output Parameter: • recvbuf: address of receive buffer (significant only at root)

  5. Code #include <mpi.h> #include <stdio.h> main (int argc,char *argv[]){ int i, rank, a[15], b[3], psum, c[5], tsum; MPI_Init (&argc,&argv); MPI_Comm_rank (MPI_COMM_WORLD,&rank); if(rank==0) for(i=0;i<15;i++){ printf(“#%d:Enter number: ”,i); scanf(“%d”,&a[i]);} MPI_Scatter (a,3,MPI_INT,b,3,MPI_INT,0,MPI_COMM_WORLD); psum=0; for(i=0;i<3;i++) psum+=b[i]; MPI_Gather (&psum,1,MPI_INT,c,1,MPI_INT,0,MPI_COMM_WORLD); if(rank==0){ tsum=0; for(i=0;i<5;i++) tsum+=c[i]; printf (“sum of the vector is %d\n”,tsum);} MPI_Finalize();}

  6. Assignment • Write and explain the argument lists of the following and say how they are different from the two functions you have seen: • MPI_Gatherv • MPI_Scatterv • MPI_Allgather • MPI_Allgatherv • MPI_Alltoall • MPI_Alltoallv

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