!Homework 7
!Programmer: Chad Brewbaker
!Email address: crb002@iastate.edu
!Date: Febuary 25, 2004
!Machine used: hpc-class.iastate.edu (Intel Xenon cluster)
!Compiler options used:

program
implicit none
integer, parameter :: n=3
real*8::A(1:n),B(1:n),C(1:n)
include "mpif.h"
integer::i,j,ierror,p,rank,status(mpi_status_size)
call mpi_init(ierror)
call mpi_comm_size(mpi_comm_world,p,ierror)
call mpi_comm_rank(mpi_comm_world,rank,ierror)

do i=1,n
   A(i)=float(i)+rank
   B(i)=-A(i)
enddo
print *,'Before the shift on processor ',rank,' A= ',A
print *,'Before the shift on processor ',rank,' B= ',B

!If p==1 do nothing
if(p.ne.1)then
      call MPI_Sendrecv_replace(A(1),n,MPI_REAL8,modulo(rank+1,p),1,modulo(rank-1,p),1,MPI_COMM_WORLD,status,ierror)
!!$   Different tags so we shouldn't need to call MPI_Barrier(MPI_COMM_WORLD,ierror)
      call MPI_Sendrecv_replace(B(1),n,MPI_REAL8,modulo(rank-1,p),2,modulo(rank+1,p),2,MPI_COMM_WORLD,status,ierror)
endif
print *,'After the shift on processor ',rank,' A= ',A
print *,'After the shift on processor ',rank,' B= ',B
call MPI_Finalize(ierror)
end program
!!$vincent% mpirun -np 4 hw7.exe
!!$ Before the shift on processor            1  A=    2.00000000000000     
!!$   3.00000000000000        4.00000000000000     
!!$ Before the shift on processor            1  B=   -2.00000000000000     
!!$  -3.00000000000000       -4.00000000000000     
!!$ Before the shift on processor            3  A=    4.00000000000000     
!!$   5.00000000000000        6.00000000000000     
!!$ Before the shift on processor            3  B=   -4.00000000000000     
!!$  -5.00000000000000       -6.00000000000000     
!!$ Before the shift on processor            0  A=    1.00000000000000     
!!$ After the shift on processor            3  A=    3.00000000000000     
!!$ After the shift on processor            1  A=    1.00000000000000     
!!$ Before the shift on processor            2  A=    3.00000000000000     
!!$   2.00000000000000        3.00000000000000     
!!$ Before the shift on processor            0  B=   -1.00000000000000     
!!$  -2.00000000000000       -3.00000000000000     
!!$ After the shift on processor            0  A=    4.00000000000000     
!!$   5.00000000000000        6.00000000000000     
!!$ After the shift on processor            0  B=   -2.00000000000000     
!!$  -3.00000000000000       -4.00000000000000     
!!$   2.00000000000000        3.00000000000000     
!!$ After the shift on processor            1  B=   -3.00000000000000     
!!$  -4.00000000000000       -5.00000000000000     
!!$   4.00000000000000        5.00000000000000     
!!$ Before the shift on processor            2  B=   -3.00000000000000     
!!$  -4.00000000000000       -5.00000000000000     
!!$ After the shift on processor            2  A=    2.00000000000000     
!!$   3.00000000000000        4.00000000000000     
!!$ After the shift on processor            2  B=   -4.00000000000000     
!!$  -5.00000000000000       -6.00000000000000     
!!$   4.00000000000000        5.00000000000000     
!!$ After the shift on processor            3  B=   -1.00000000000000     
!!$  -2.00000000000000       -3.00000000000000     
!!$vincent%