Sure it helps. I had no idea about this source. I hope that it is up to date.
2010/12/13 Gus Correa <g...@ldeo.columbia.edu> > Hi Kechagias > > The figures in Chapter 4 of > "MPI: The Complete Reference, Vol 1, 2nd Ed.", > by Snir et. al. are good reminders. > > Here are a few: > //www.dartmouth.edu/~rc/classes/intro_mpi/mpi_comm_modes2.html#top > > I hope this helps, > Gus Correa > > Kechagias Apostolos wrote: > >> 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 <mailto: >> 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 <mailto: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 <mailto:us...@open-mpi.org> >> >> http://www.open-mpi.org/mailman/listinfo.cgi/users >> >> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/users >> > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users >
