[mpich-discuss] (no subject)

["Antonio J. Peña"]

Dear user,

Please note that this mailing list is exclusively intended to discuss 
potential issues with the MPICH MPI implementation. Since your question 
is about general MPI usage, we cannot provide you with that assistance 
here. You will surely find assistance in this kind of topics in general 
programming forums such as stackoverflow, where some of our team members 
contribute as well. Also, web search engines are likely to be a good 
resource in your case.

Best regards,
   Antonio


On 12/05/2014 11:50 AM, Chafik sanaa wrote:
> I have a table "tab[]" with 10 elements "0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 
> | 8 | 9 |" I am sending with the Scatterv function; 4 elements to the 
> process 0 "|0 | 1 | 2 | 3 | 4| "and 6 elements to process 1 "| 5 | 6 | 
> 7 | 8 | 9 | ", after I did the summation of the value" add " to each 
> element of the received table which gives me a new table "afteradd[] 
> "for each process, I want this time collecting the both tables 
> "afteradd[]" and send them to the process 0, after a little research I 
> found that there's a GATHERV function which do that but I do not know 
> how ?
> program:
> #include <malloc.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <time.h>
> #include "math.h"
> #include "mpi.h"
>
> int main(int argc, char** argv)
> {
> int    taskid, ntasks;
> int    ierr, i, itask;
> intsendcounts[2048], displs[2048], recvcount;
> double     **sendbuff, *recvbuff,*afteradd, buffsum, buffsums[2048];
> double     inittime, totaltime;
> const int nbr_etat = 10;
> double tab[nbr_etat];
> for (int i = 0; i < nbr_etat; i++)
> tab[i] = i;
> int nbr_elm[2] = { 4, 6 };
> int dpl[2] = { 0, 4 };
> MPI_Init(&argc, &argv);
> MPI_Comm_rank(MPI_COMM_WORLD, &taskid);
> MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
> recvbuff = (double *)malloc(sizeof(double)*nbr_etat);
> if (taskid == 0)
> {
> sendbuff = (double **)malloc(sizeof(double *)*ntasks);// run for 2 proc
> sendbuff[0] = (double *)malloc(sizeof(double)*ntasks*nbr_etat);
> for (i = 1; i < ntasks; i++)
> {
> sendbuff[i] = sendbuff[i - 1] + nbr_etat;
> }
> }
> else
> {
> sendbuff = (double **)malloc(sizeof(double *)* 1);
> sendbuff[0] = (double *)malloc(sizeof(double)* 1);
> }
>
> if (taskid == 0){
>
> srand((unsigned)time(NULL) + taskid);
> for (itask = 0; itask<ntasks; itask++)
> {
> int k;
> displs[itask] = itask*nbr_etat;
> int s = dpl[itask];
> sendcounts[itask] = nbr_elm[itask];
>
>
> for (i = 0; i<sendcounts[itask]; i++)
> {
> k = i + s;
> sendbuff[itask][i] = tab[k];
> printf("+ %0.0f  ", sendbuff[itask][i]);
> }
> printf("\n");
> }
> }
>
> recvcount = nbr_elm[taskid];
>
> inittime = MPI_Wtime();
>
> ierr = MPI_Scatterv(sendbuff[0], sendcounts, displs, MPI_DOUBLE,
> recvbuff, recvcount, MPI_DOUBLE,
> 0, MPI_COMM_WORLD);
>
> totaltime = MPI_Wtime() - inittime;
>
> buffsum = 0.0;
> int add = 3;
> afteradd = (double *)malloc(sizeof(double)*nbr_etat);
> for (i = 0; i<recvcount; i++)
> {
> afteradd [i]= add + recvbuff[i];
> }
> for (i = 0; i<recvcount; i++)
> {
> printf("* %0.0f", afteradd[i]);
> }
> printf("\n");
> if (taskid == 0)
> {
> free(sendbuff[0]);
> free(sendbuff);
> }
> else
> {
> free(sendbuff[0]);
> free(sendbuff);
> free(recvbuff);
> }
> MPI_Finalize();
>
> }
>
>
>
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-- 
Antonio J. Peña
Postdoctoral Appointee
Mathematics and Computer Science Division
Argonne National Laboratory
9700 South Cass Avenue, Bldg. 240, Of. 3148
Argonne, IL 60439-4847
apenya at mcs.anl.gov
www.mcs.anl.gov/~apenya

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