Arunkumar C R wrote:
Hi,
A fortran 90 code having MPI enabled subroutine is written. The
subroutine part is given below,
program abc
.................. !usual statements
open(20, file='sum.20', action='write')
open(30, file='sum.40', action='write')
n2= 100; nstep=50
do step=1, nstep
n1 = step
sum2 = (n2 - n1 + 1) * (2*n1 + (n2 - n1 )) /
2 !from arithmetic progression
call routine
write(20, *) step, sum1, sum2
end do
end program abc
subroutine routine
use
dat
!module 'dat' with common variables for both program & subroutine
use mpi
implicit none
integer::ivar, istart, iend, sumt, i
if(step.eq.1) call mpi_init(ierr)
call mpi_comm_rank(mpi_comm_world, irank, ierr)
call mpi_comm_size(mpi_comm_world, np, ierr)
ivar = (n2 - n1) / np + 1
istart= min(irank * ivar + 1, n2 + 1)
iend = min(istart + ivar - 1, n2)
sum1 = 0
do i=istart, iend
sum1= sum1 + i
end do
call mpi_reduce(sum1, sumt, 1, mpi_integer, mpi_sum, 0,
mpi_comm_world, ierr)
sum1 = sumt
if(irank.eq.0) then
write(30, *) step, sum1, sum2
end if
if(step.eq.nstep) call mpi_finalize(ierr)
end subroutine routine
The current problem is that once the subroutine is called the data
written to sum.30 and sum.20 are not matching.
If there's no mistake with the calculation part, how shall it be
possible to get the same data in both the files. I could
see some of the 'sum1' values in sum.20 are not correct.
First, can you confirm that sum.30 is correct? You should be able to
judge each output file independently, and not simply compare the two to
each other.
One of the problems with sum.20 is that it is being (over?)written by
multiple processes. When you launch the (multi-process MPI) job with
mpirun, you start multiple copies of the executable. So, multiple
processes are opening the files and writing to sum.20. You need a
statement in the main program like the "if(irank.eq.0)" conditional in
the subroutine.
I don't know what errors, exactly, you're seeing. So, I don't know if
that addresses all of your problems. But this is certainly one of them.
