MPI_Allgather receiving junk - fortran

Question

I have the following code:
real :: s_s, d_s, s_r(size), d_r(size)
integer :: k, k_r(size)
! - size = number of processors
! - Do something to initialise s_s, d_s, k
write(*,*) "SENDING >>>>"
write(*,*) s_s, d_s
call MPI_Allgather( s_s, 1, MPI_REAL,
& s_r, 1, MPI_REAL, MPI_COMM_PGM, mpi_err)
call MPI_Allgather( d_s, 1, MPI_REAL,
& d_r, 1, MPI_REAL, MPI_COMM_PGM, mpi_err)
call MPI_Allgather ( k, 1, MPI_INTEGER,
& k_r, 1, MPI_INTEGER, MPI_COMM_PGM, mpi_err)
write(*,*) "RECEIVED <<<<"
write(*,*) s_r, d_r, kr
This generates the following output:
SENDING >>>>
-1803.80339864908 0.616157856320407
RECEIVED <<<<
6.953077622513053E-310 3.565412685916647E-314 1.221334434576037E-314
1.498827614035474E-314 6.952991536467244E-310 6.953288052096687E-310
6.953108563966064E-310 2.350861403096908E-314 4 1
2 3
kr is being gathered correctly however, s_r and d_r seem to be receiving junk. Could this be because of the MPI datatypes? I tried with MPI_REAL MPI_REAL8 and MPI_DOUBLE but that didn't work. Furthermore, mpi_err = MPI_SUCCESS
What could I do to resolve this?
EDIT 1
I worked on the following prototype program:
program allgather
implicit none
include "mpif.h"
real a(4)
integer rank,size,ierr
real as(4)
real ar(16)
integer i, j, k,z
a=1
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD, size, ierr)
if(size.ne.4)then
write(*,*)'Error!:# of processors must be equal to 4'
write(*,*)'Programm aborting....'
call MPI_ABORT(ierr)
endif
do k=1,4
if ( rank == (mod(k, size))) then
a(k) = k
else
a(k) = 0.0
endif
enddo
write(*,*) "Rank :", rank
write(*,*) a
call MPI_Allgather(a, 4, MPI_REAL, ar,
& 4,
& MPI_REAL, MPI_COMM_WORLD, ierr)
write(*,*) "Recieved array"
write(*,*) ar
do i = 1, 16
if ( ar(i) /= 0.0 ) then
z = mod(i, size)
if ( z == 0 ) then
a( size ) = ar(i)
else
a ( z ) = ar(i)
endif
endif
enddo
write(*,*) "---------"
write(*,*) a
write(*,*) "---------"
call MPI_FINALIZE(ierr)
end
And this generates the expected results i.e. ar doesn't gather junk. I'm unable to however tell the difference between the implementations.

Answer 1

It turns out that for the project, the data type to be used was MPI_FLT. It is strange that MPI_FLT works and not MPI_REALx where x=4,8 also not MPI_FLOAT. I grep-ed MPI_FLT in the project to see what it is defined as but didn't turn up anywhere in the project.
The OpenMPI version I'm using is:
$ mpirun --version
mpirun (Open MPI) 3.0.0
The compiler I use is:
$ mpifort --version
ifort (IFORT) 19.0.1.144 20181018
In a future edit I will elaborate on the cause.