I thought that every process will receive the data as is. Thanks that solved my problem.
2010/12/13 Gus Correa <g...@ldeo.columbia.edu> > Kechagias Apostolos wrote: > >> I have the code that is in the attachment. >> Can anybody explain how to use scatter function? >> It seems that this way im using it doesnt do the job. >> >> >> ------------------------------------------------------------------------ >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/users >> > #include <stdio.h> > #include <stdlib.h> > #include <string.h> > #include <mpi.h> > > int main(int argc, char *argv[]) > { > int error_code, err, rank, size, N, i, N1, start, end; > > float W, pi=0, sum=0; > > > > MPI_Init(&argc, &argv); > MPI_Comm_rank( MPI_COMM_WORLD, &rank); > MPI_Comm_size( MPI_COMM_WORLD, &size); > > N=atoi(argv[1]); > > int n[N],data[N]; > > N1 = N/size; > W=1.0/N; > //printf("N1:%d W:%f\n",N1,W); > > > > if(size<2) > { > printf("You must have 2 or more ranks to complete this > action\n"); > MPI_Abort(MPI_COMM_WORLD,err); > } > if(argc<2) > { > printf("Not enough arguments given\n"); > MPI_Abort(MPI_COMM_WORLD,err); > } > > > > if(rank == 0) {for(i=0;i<N;i++) n[i]=i;} > > MPI_Scatter (n, N1, MPI_INT,data, N1,MPI_INT, 0, MPI_COMM_WORLD); > > pi = 0; > > start = rank*N1; > end = (rank+1)*N1; > > for(i=data[start];i<data[end];i++) pi+=4*W/(1+(i+0.5)*(i+0.5)*W*W); > // printf("rank:%d tmppi:%f\n",rank,pi); > printf("data[start]:%d data[end]:%d ",data[start],data[end]); > > printf("rankN1:%d rank+1N1:%d\n",start,end); > MPI_Reduce(&pi, &sum, 1, MPI_FLOAT, MPI_SUM, 0, MPI_COMM_WORLD); > > > if (rank == 0) printf("Pi is:%f size:%d\n",sum,size); > > MPI_Finalize(); > } > > > ######### > Hi Kechagias > > If you use MPI_Scatter, the receive buffers start receiving > at the zero offset (i.e. at data[0]), not at data[start]. > Also, your receive buffers could have size N1, not N. > I guess the MPI_Scatter call is right. > The subsequent code needs to change. > The loop should go from data[0] to data[N1-1]. > (However, be careful with edge cases where the number > of processes doesn't divide N evenly.) > > Alternatively you could use MPI_Alltoallw to scatter the way > your code suggests you want to do, but that would be an overkill. > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users >
