Fortran subroutine returning wrong values

Question

Hey I'm working on a fortran program and have ran across an odd problem. When I try to output some values of an array directly before calling a specific subroutine I get the correct values. I then try to output some values of the same array right as I start the subroutine, and they are 0. I finally output the values of the array after the subroutine and the values are back to the expected values. Could anyone help me understand why? My code is below:

First, the calling of the subroutine in the main function, with values I want outputted in the write statements:

if (iter .eq. 5) then
  write(*,*) 'vp vals: ',vp(0,23471), vp(0,23475)
end if 

CALL GRID_DIVISION( &
&            NPTMAX, DIM, TYPEMAX, NEIGHMAX, NPTC, GRIDLIMIT, &
&            GRIDN, GRIDNUM, GRID, GNEIGH, XP, PTTYPE, TYPE, &
&            GRIDP, TEMP_GRIDP, GNEIGHMAX, PAINT, VP, ITER, gridvel &
&          )

if (iter .eq. 5) then
  write(*,*) 'vp vals: ',vp(0,23471), vp(0,23475)
end if 

This is calling the following subroutine, of which I will post only the relevant part:

SUBROUTINE GRID_DIVISION( &
&            NPTMAX, DIM, TYPEMAX, NEIGHMAX, NPTC, GRIDLIMIT, &
&            GRIDN, GRIDNUM, GRID, GNEIGH, XP, PTTYPE, TYPE, &
&            GRIDP, TEMP_GRIDP, GNEIGHMAX, PAINT,VP,ITER, gridvel &
&          )
  IMPLICIT NONE
  INTEGER, INTENT(IN)    :: NPTMAX, DIM, TYPEMAX, NEIGHMAX, GNEIGHMAX
  INTEGER, INTENT(IN)    :: NPTC
  INTEGER, INTENT(IN)    :: GRIDLIMIT
  INTEGER, INTENT(IN)    :: GRIDN(0: DIM - 1)
  INTEGER, INTENT(IN)    :: GRIDNUM
  INTEGER, INTENT(IN)    :: PTTYPE(0: NPTMAX)
  INTEGER, INTENT(IN)    :: TYPE(0: TYPEMAX)
  INTEGER, INTENT(INOUT) :: GRIDP(0: NPTMAX)
  INTEGER, INTENT(INOUT) :: GNEIGH(1: GRIDLIMIT, 0: GNEIGHMAX)
  REAL   , INTENT(IN)    :: GRID(1: GRIDLIMIT, 0: DIM - 1, 0: 1)
  REAL   , INTENT(IN)    :: XP(0: DIM - 1, 0: NPTMAX)
  REAL   , INTENT(IN)    :: VP(0: DIM - 1, 0: NPTMAX)
  INTEGER, INTENT(INOUT) :: TEMP_GRIDP(0: NPTMAX)
  INTEGER, INTENT(INOUT) :: PAINT(0:NPTMAX)
  INTEGER, INTENT(INOUT) :: ITER
  real, intent(inout)    :: gridvel(GRIDNUM,0:1)
  INTEGER :: II, JJ, KK
  INTEGER :: DNUM
  INTEGER :: GRIDXP
  INTEGER :: SGRIDXP
  INTEGER :: EGRIDXP
  INTEGER :: SGRIDYP
  INTEGER :: EGRIDYP
  INTEGER :: SEARCH
  INTEGER :: SCOUNT
  INTEGER :: FCOUNT
  INTEGER :: ERROR
  INTEGER, PARAMETER :: CELL = 2 

  if (iter .eq. 5) then
    write(*,*) 'vp vals: ',vp(0,23471), vp(0,23475)
  end if 
...
end subroutine

With more stuff after this section which is not ouputted. When I run the code my outputs on iteration 5 for this section are:

vp vals:    75.00000        75.00000
vp vals:     0.00000000E+00  0.0000000E+00
vp vals:    75.00000        75.00000

I simply can't figure out why my array VP does not have values in the subroutine.

Answer 1

I figured it out. VP was allocated as

VP(0:DIM,0:NPTMAX) 

in the main program and

VP(0:DIM-1,0:NPTMAX) 

in the subroutine! This caused the error.