[mpich-discuss] (no subject)

[Chafik sanaa]

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;
int         sendcounts[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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