!Homework 6
!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)
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)

call random_number(A)
A=A+rank
print *,'Before the shift on processor ',rank,' A= ',A

!Evens send to odds then recive
!Odds recive, then send to evens.
!If p==1 do nothing
if(p.ne.1)then
   if(mod(p,2)==0)then
      call MPI_send(A(1),n,MPI_REAL8,modulo(rank+1,p),1,MPI_COMM_WORLD,ierror)
      call MPI_recv(A(1),n,MPI_REAL8,modulo(rank-1,p),1,MPI_COMM_WORLD,status,ierror)
   else
      call MPI_recv(B(1),n,MPI_REAL8,modulo(rank-1,p),1,MPI_COMM_WORLD,status,ierror)
      call MPI_send(A(1),n,MPI_REAL8,modulo(rank+1,p),1,MPI_COMM_WORLD,ierror)
      A=B
   endif
endif
print *,'After the shift on processor ',rank,' A= ',A
call MPI_Finalize(ierror)
end program

!!$vincent% mpirun -np 4 hw6.exe
!!$ Before the shift on processor            1  A=    1.77326712988589     
!!$   1.82325123434867        1.14812062030844     
!!$ Before the shift on processor            2  A=    2.77326712988589     
!!$   2.82325123434867        2.14812062030844     
!!$ After the shift on processor            2  A=    1.77326712988589     
!!$   1.82325123434867        1.14812062030844     
!!$ Before the shift on processor            3  A=    3.77326712988589     
!!$   3.82325123434867        3.14812062030844     
!!$ After the shift on processor            3  A=    2.77326712988589     
!!$   2.82325123434867        2.14812062030844     
!!$ After the shift on processor            1  A=   0.773267129885890     
!!$ Before the shift on processor            0  A=   0.773267129885890     
!!$  0.823251234348674       0.148120620308437     
!!$ After the shift on processor            0  A=    3.77326712988589     
!!$   3.82325123434867        3.14812062030844     
!!$  0.823251234348674       0.148120620308437     
!!$vincent%