Variable value is dependent on WRITE statement?!

[stepanenatsrccdotmsu]

Hi everybody,

I faced a "strange" behaviour of my Fortran program. It is MPI program of >50000 strings code.
I found that the values of array elements are dependent whether I write them by

write(*,*) 'phisuf22 = ', phisuf(ix,iy)

or not. If I make this WRITE the values of the array are those that are expected from arithmetics
used to calculate phisuf(ix,iy). If I do not make this WRITE the values are several order of
magnitude different. Of cource it is inpractical to make this WRITE only to "correct" calculations.
I guess this can be an issue of memory. I tried -check all compiler option but no error message appeared.
My compiler is Intel 12.0.

Has anybody an idea how to handle this problem?

Many thans in advance,
Victor, Moscow.

[mecej4]

Which compiler options did you use? Does the error occur with optimization turned off?

How do you check the values of phisuf when there are no print statements to display those values?

Can you post a small example that captures the kind of behavior that you see?

[stepanenatsrccdotmsu]

I compile multiple source files as follows

mpif90 -O3 -c -fpp -module /home/users/stepanenko/

nh3dmpi/modules par_ex.f -o /home/users/stepanenko/nh3dmpi/objfiles/par_ex.o

The error does not occur when I exclude -O3 option.

I check values of phisuf by calling a subroutine that writes the whole array to a file.

Below is the header of my subroutine, declarations and the cycle computing
phisuf. In the cycle you see WRITE statement which "causes" the change
of phisuf values.

[fortran]  SUBROUTINE SURPHN_MPI &

      &(nx, ny, nx1, ny1, nchn1, verbose, &

      & phisuf, dpdx10, dpdy01, tsuf, tsufi, psuf, psufi, hsuf, &

      & dphsdx, dphsdy, &

      & eigxy, trigsx, trigsy, &

      & sipcox, simcox, sipcoy, simcoy, &

      & ifax, ifay, &

      & dx, dy, dxx, dyy, &

      & phsout, prt)



! the following code performs the solution of the elliptic problem

! for the surface boundary condition for phis, using neuman non-

! -homogeneous boundary conditions, and integrates the hydrostatic

! equation to get phis everywhere.



!-----------------------------------------------------------------------

! re-evaluate reference state variables and compute phi at surface

! with pts prespecified

!-----------------------------------------------------------------------



      use ALLOC, only : &

      & r05, g



      use MPI_VARIABLES, only : &

      & nxs2i, nxs2e, nys2i, nys2e, &

      & nxi, nxe, nyi, nye, &

      & nx0i, nx1e, ny0i, ny1e, &

      & xlbound, xrbound, ylbound, yrbound, &

      & size_MPI, comm3d, rank_comm3d



      implicit none



!      include 'nh3dpa10.inc'

!      common/bphi/ dphsdx(2,0:ny1),dphsdy(0:nx1,2)

!      dimension hk11(0:nx1,0:ny1),hk12(0:nx1,0:ny1)



!-----------------------------------------------------------------------

!     reevaluate variables of reference state from new pp(i,3)

!-----------------------------------------------------------------------

!-----------------------------------------------------------------------

! calculate bottom b.c. for phis from new surface pressure.

! solves poisson equation for surface phis, with neuman b.c.

! following williams (jfm,1969). both the diagnostic equation for

! phisuf and its lateral boundary conditions are imposed by pp.

!-----------------------------------------------------------------------



      ! Input/output variables

      integer(4), intent(in) :: nx, ny, nx1, ny1

      integer(4), intent(in) :: nchn1, verbose



      real(8), intent(inout) :: phisuf(nxs2i:nxs2e,nys2i:nys2e)

      real(8), intent(in) :: dpdx10(nxs2i:nxs2e,nys2i:nys2e,3:3)

      real(8), intent(in) :: dpdy01(nxs2i:nxs2e,nys2i:nys2e,3:3)

      real(8), intent(in) :: tsuf(nxs2i:nxs2e,nys2i:nys2e)

      real(8), intent(in) :: tsufi(nxs2i:nxs2e,nys2i:nys2e)

      real(8), intent(in) :: psuf(nxs2i:nxs2e,nys2i:nys2e)

      real(8), intent(in) :: psufi(nxs2i:nxs2e,nys2i:nys2e)

      real(8), intent(in) :: hsuf(nxs2i:nxs2e,nys2i:nys2e)

      real(8), intent(inout) :: dphsdx(1:2,nys2i:nys2e)

      real(8), intent(inout) :: dphsdy(nxs2i:nxs2e,1:2)  



      real(8), intent(inout) :: eigxy(2:nx,2:ny)

      real(8), intent(inout) :: trigsx(1:nx-1), trigsy(1:ny-1)

      real(8), intent(inout) :: sipcox(1:nx-1), simcox(1:nx-1)

      real(8), intent(inout) :: sipcoy(1:ny-1), simcoy(1:ny-1)

      

      integer(4), intent(inout) :: ifax(1:10), ifay(1:10)



      real(8), intent(in) :: dx, dy, dxx, dyy



      logical, intent(in) :: phsout, prt



      ! Local variables

      integer(4) :: ix, iy

      integer(4) :: i0, j0

      integer(4) :: k19

      integer(4) :: isend



      real(8), allocatable :: hk11(:,:), hk12(:,:)



      real(8) :: phsfco

      real(8) :: tk





      do iy = max(nyi,2), nye ! 2, ny

      do ix = max(nxi,2), nxe ! 2, nx

        phisuf(ix,iy) = -r05*( &

        & (dpdx10(ix,iy,3)*(tsuf(ix+1,iy)/psuf(ix+1,iy)+tsuf(ix,iy) &

        & /psuf(ix,iy)) &

        & -dpdx10(ix-1,iy,3)*(tsuf(ix,iy)/psuf(ix,iy)+tsuf(ix-1,iy) &

        & /psuf(ix-1,iy)))/dx &

        & +(dpdy01(ix,iy,3)*(tsuf(ix,iy+1)/psuf(ix,iy+1)+tsuf(ix,iy) &

        & /psuf(ix,iy)) &

        & -dpdy01(ix,iy-1,3)*(tsuf(ix,iy)/psuf(ix,iy)+tsuf(ix,iy-1) &

        & /psuf(ix,iy-1)))/dy)

         ! THIS OUTPUT CAUSES CHANGE OF PHISUF VALUE
         ! if (ix == 2 .and. iy == 2) write(*,*) 'phisuf22 = ', phisuf(ix,iy)
      enddo

      enddo[/fortran]