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POHow to divide work between processes in MPI
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  1. POHow to divide work between processes in MPI
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    copied!<p>I have the following code to count the number of primes, I have divided the work in the loop across processors. The problem is that when the subroutine assigns sub-sections of the loop to processors it assigns according to rank and i cant seem to control the order in which they arrive </p> <p>i.e i would like then to come as 0,1,2,3... and not like 2,1,0,3..</p> <p>So that if there were 500 iterations in the loop and 5 processors. </p> <ul> <li>Rank 0 executes [1 - 100]</li> <li><p>Rank 1 executes [101-200] etc...</p> <pre><code> program main implicit none include 'mpif.h' integer(4), parameter :: n = 36500 integer(4) :: a(n) integer(4) :: i integer(4) :: j integer(4) :: ista integer(4) :: iend integer(4) :: sum integer(4) :: f=0 integer(4) :: ssum integer(4) :: ierr integer(4) :: iproc integer(4) :: nproc call MPI_INIT(ierr) call MPI_COMM_SIZE(MPI_COMM_WORLD, nproc, ierr) call MPI_COMM_RANK(MPI_COMM_WORLD, iproc, ierr) call loop_range(2, n, nproc, iproc, ista, iend) sum = 0.0 print *,ista,"-",iend,"&gt;",iproc do i = ista, iend f=0 do j=2,INT(SQRT(REAL(i))) if(MOD(i,j)==0) then f=1 end if end do if(f==0) then sum = sum + 1 end if end do call MPI_REDUCE(sum, ssum, 1, MPI_INTEGER,MPI_SUM, 0,MPI_COMM_WORLD, ierr) if ( iproc == 0 ) write(6,*)'Total No of primes=', ssum call MPI_FINALIZE(ierr) end program main subroutine para_range(n1, n2, nprocs, irank, ista, iend) integer(4) :: n1 ! Lowest value of iteration variable integer(4) :: n2 ! Highest value of iteration variable integer(4) :: nprocs ! No of Cores/Processors you want to use integer(4) :: irank ! Process rank integer(4) :: ista ! Start of iterations for rank iproc integer(4) :: iend ! End of iterations for rank iproc integer(4) :: iwork1, iwork2 print *,irank iwork1 = ( n2 - n1 + 1 ) / nprocs iwork2 = MOD(n2 - n1 + 1, nprocs) ista = irank * iwork1 + n1 + MIN(irank, iwork2) iend = ista + iwork1 - 1 if ( iwork2 &gt; irank ) then iend = iend + 1 end if end subroutine para_range </code></pre></li> </ul> <p>I am using Open MPI.</p>
 

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