program mpi_test2

!	test to show updating for i,j double loop (partial continuous data) for specific req data only

!	ie update u(2:6,2:6) values instead of all u values, also for struct data

!	FVM use

implicit none

include "mpif.h"	

integer, parameter :: size_x=8,size_y=8

integer :: i,j,k,ierr,rank,nprocs,u(size_x,size_y)

integer :: jsta,jend,jsta2,jend1,inext,iprev,isend1,irecv1,isend2

integer :: irecv2,is,ie,js,je

integer, allocatable :: jjsta(:), jjlen(:),jjreq(:),u_tmp(:,:)

INTEGER istatus(MPI_STATUS_SIZE)



call MPI_Init(ierr)

call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
  
call MPI_Comm_size(MPI_COMM_WORLD,nprocs,ierr)

allocate (jjsta(0:nprocs-1),jjlen(0:nprocs-1),jjreq(0:nprocs-1))

is=3;	ie=6;	js=3;	je=6

allocate (u_tmp(is:ie,js:je))



do k = 0, nprocs - 1

	call para_range(js,je, nprocs, k, jsta, jend)

	jjsta(k) = jsta
	
	jjlen(k) = (ie-is+1) * (jend - jsta + 1)

end do

call para_range(js, je, nprocs, rank , jsta, jend)

do j=jsta,jend

	do i=is,ie

		u(i,j)=(j-1)*size_x+i

		

	end do

end do

do j=jsta,jend

	do i=is,ie

		u_tmp(i,j)=u(i,j)

		

	end do

end do

do k=0,nprocs-1

	call MPI_Barrier(MPI_COMM_WORLD,ierr)

	if (k==rank) then

		print *, rank

		write (*,'(8i5)') u

		

	end if

end do

do k = 0, nprocs - 1

	

	call MPI_BCAST(u_tmp(is,jjsta(k)), jjlen(k), MPI_Integer,k, MPI_COMM_WORLD, ierr)

end do




deallocate (jjsta, jjlen, jjreq)

u(is:ie,js:je)=u_tmp(is:ie,js:je)



do k=0,nprocs-1

	call MPI_Barrier(MPI_COMM_WORLD,ierr)

	if (k==rank) then

		print *, rank

		write (*,'(8i5)') u

		

	end if

end do




call MPI_Finalize(ierr)

contains

subroutine para_range(n1, n2, nprocs, irank, ista, iend)
!	block distribution

integer n1 !The lowest value of the iteration variable (IN)

integer n2 !The highest value of the iteration variable (IN)

integer nprocs !The number of processes (IN)

integer irank !The rank for which you want to know the range of iterations(IN)

integer ista !The lowest value of the iteration variable that process irank executes (OUT)

integer iend !The highest value of the iteration variable that process irank executes (OUT)

integer iwork1,iwork2

iwork1 = (n2 - n1 + 1) / nprocs

iwork2 = mod(n2 - n1 + 1, nprocs)

ista = irank * iwork1 + n1 + min(irank, iwork2)

iend = ista + iwork1 - 1

if (iwork2 > irank) iend = iend + 1

end subroutine para_range

end program mpi_test2