Reading data from files using MPI in Fortran - fortran

Question

I want to read data from some .dat files to a Fortran code for postprocessing. As a test case, I am just using one processor for MPI and trying to read single data file to my code. The content of the data file is as follows:
qout0050.dat : 1 1 1
However, the matrix (Vn in this case) which is supposed to store the content of this data file shows all 0 values. The relevant part of the code which reads from data file and store to the matrix is as follows:
subroutine postproc()
use precision_mod
use mpicomms_mod
implicit none
integer(kind=MPI_Offset_kind) :: i, j , igrid, k, l, disp, iproc, info, lwork
integer :: rst, numvar, ifile, number, num, step, ntot
integer :: Nx_max, Ny_max, Nz_max
integer :: Nxp, Nzp, Nyp, Ngrid
integer :: Ifirst, Ilast, Jfirst, Jlast, Kfirst, Klast
character*(64) :: fname, buffer, ffname
integer :: tmp, N1, N2, N3, tmpp
real(WP), allocatable :: qout(:,:,:,:), phi_xyz(:,:,:,:,:)
real(WP), allocatable :: Vn(:,:), Vntmp(:,:), TAU(:,:)
real(WP), allocatable :: Rprime(:,:), Rtmp(:,:), Rend(:,:), Q(:,:), tmpL(:), tmpG(:)
real(WP), allocatable :: s(:), vt(:,:), u(:,:), utmp(:,:)
real(WP), allocatable :: tmp1(:,:), tmp2(:,:), tmp3(:,:), phi(:,:)
integer, dimension(2) :: view
integer :: view1
integer, dimension(3) :: lsizes, gsizes, start
real(WP) :: tmpr
real(WP), allocatable :: work(:), mu(:), eigY(:,:), wr(:), wi(:), beta(:)
integer(kind=MPI_Offset_kind) :: SP_MOK, Nx_MOK, Ny_MOK, Nz_MOK, WP_MOK
open(unit=110,file='postparameters.dat',form="formatted")
read (110,*) Nx_max
read (110,*) Ny_max
read (110,*) Nz_max
read (110,*) numvar
read (110,*) step
close(110)
! Define the size of grid on each processor
if (mod(Nx_max,px).ne.0) then
write(*,*) 'Error in preproc: Nx_max is not devisable by px'
call MPI_ABORT(MPI_COMM_WORLD,0,ierr)
end if
Nxp = Nx_max/px
if (mod(Ny_max,py).ne.0) then
write(*,*) 'Error in preproc: Nx_max is not devisable by px'
call MPI_ABORT(MPI_COMM_WORLD,0,ierr)
end if
Nyp = Ny_max/py
if (mod(Nz_max,pz).ne.0) then
write(*,*) 'Error in preproc: Nx_max is not devisable by px'
call MPI_ABORT(MPI_COMM_WORLD,0,ierr)
end if
Nzp = Nz_max/pz
Ifirst = irank*Nxp + 1
Ilast = Ifirst + Nxp - 1
Jfirst = jrank*Nyp + 1
Jlast = Jfirst + Nyp - 1
Kfirst = krank*Nzp + 1
Klast = Kfirst + Nzp - 1
! Setting the view for phi
gsizes(1) = Nx_max
gsizes(2) = Ny_max
gsizes(3) = Nz_max
lsizes(1) = Nxp
lsizes(2) = Nyp
lsizes(3) = Nzp
start(1) = Ifirst - 1
start(2) = Jfirst - 1
start(3) = Kfirst - 1
call MPI_TYPE_CREATE_SUBARRAY(3,gsizes,lsizes,start,&
MPI_ORDER_FORTRAN,MPI_REAL_SP,view,ierr)
call MPI_TYPE_COMMIT(view,ierr)
call MPI_TYPE_CREATE_SUBARRAY(3,gsizes,lsizes,start,&
MPI_ORDER_FORTRAN,MPI_REAL_WP,view1,ierr)
call MPI_TYPE_COMMIT(view1,ierr)
WP_MOK = int(8, MPI_Offset_kind)
Nx_MOK = int(Nx_max, MPI_Offset_kind)
Ny_MOK = int(Ny_max, MPI_Offset_kind)
Nz_MOK = int(Nz_max, MPI_Offset_kind)
! Reading the qout file
ffname = 'qout'
allocate(qout(Nxp,Nyp,Nzp,numvar))
allocate(Vn(Nxp*Nyp*Nzp*numvar,step))
do rst = 1,step
if (myrank == 0) print*, 'Step = ', 50 + rst -1
write(buffer,"(i4.4)") 50 + rst -1
fname = trim(ffname)//trim(buffer)
fname = trim('ufs')//":"// trim(fname)
fname = trim(adjustl(fname))//'.dat'
call MPI_FILE_OPEN(MPI_COMM_WORLD,fname,MPI_MODE_RDONLY,MPI_INFO_NULL,ifile,ierr)
call MPI_FILE_READ(ifile,Ngrid,1,MPI_INTEGER,status,ierr)
if (1 /= Ngrid) then
if (myrank == 0 ) write(*,*) Ngrid
endif
call MPI_FILE_READ(ifile,tmp,1,MPI_INTEGER,status,ierr)
if (tmp /= Nx_max) write(*,*) tmp
call MPI_FILE_READ(ifile,tmp,1,MPI_INTEGER,status,ierr)
if (tmp /= Ny_max) write(*,*) tmp
call MPI_FILE_READ(ifile,tmp,1,MPI_INTEGER,status,ierr)
if (tmp /= Nz_max) write(*,*) tmp
call MPI_FILE_READ(ifile,tmpr,1,MPI_REAL_WP,status,ierr)
call MPI_FILE_READ(ifile,tmpr,1,MPI_REAL_WP,status,ierr)
call MPI_FILE_READ(ifile,tmpr,1,MPI_REAL_WP,status,ierr)
call MPI_FILE_READ(ifile,tmpr,1,MPI_REAL_WP,status,ierr)
do l=1,numvar
disp = 4*4 + 4*WP_MOK + Nx_MOK*Ny_MOK*Nz_MOK*WP_MOK*(l-1)
call MPI_FILE_SET_VIEW(ifile,disp,MPI_REAL_WP,view1,"native",MPI_INFO_NULL,ierr)
call MPI_FILE_READ_ALL(ifile,qout(1:Nxp,1:Nyp,1:Nzp,l),Nxp*Nzp*Nyp, MPI_REAL_WP,status,ierr)
end do
call MPI_FILE_CLOSE(ifile,ierr)
!-----------------------------------------------
! Bluiding the snapshot matrix Vn --------------
!-----------------------------------------------
do i=1,numvar
do k=1,Nzp
do j=1,Nyp
Vn((1 + Nxp*(j-1) + Nxp*Nyp*(k-1) + Nxp*Nyp*Nzp*(i-1)):(Nxp*j + Nxp*Nyp*(k-1) + Nxp*Nyp*Nzp*(i-1)),rst) = qout(1:Nxp,j,k,i)
end do
end do
end do
end do
call MPI_BARRIER(MPI_COMM_WORLD,ierr)
deallocate(qout)