Assigning array elements (Fortran)

I am having a problem getting array elements assigned. I am first trying to set all array elements to zero. The relevant code is:

  SUBROUTINE SOLVER(N_COMPS,MAX_PANS,ALPHA,U,N_OUTER,
 &   VECT_POINTS_PERP,PANEL_VECTA,DIST_POINTS,A,V_PERP,VTAN,
 &    GAMMA,N_PTS,TOT_PTS)

! IMPLICIT NONE ! INTEGER :: I, J INTEGER, INTENT(IN) :: N_COMPS,MAX_PANS, TOT_PTS

  REAL*8 :: A(N_COMPS*(MAX_PANS+1),TOT_PTS-N_COMPS)

  REAL*8 :: U_NORM((MAX_PANS*3)+N_COMPS)

! ! Initialise arrays DO I = 1, N_COMPS*(MAX_PANS+1) DO J = 1, TOT_PTS-N_COMPS A(I,J) = 0.0 ENDDO ENDDO

  DO I = 1, (MAX_PANS*3)+N_COMPS
    U_NORM(I) = 0.0
  ENDDO

When I use Checkmate to debug the code, the 'A' array has all elements set to 0.0 correctly, but the 'U_NORM' array has a random assortment of: 0.0, 'Invalid floating point number', 'Undefined', or a very small number (e.g. 2.9e-291).

I cannot see why this is occurring. Can anyone shed any light?

First if you are setting whole arrays to zero, or any other single value, then you can simply use

A=0 U_norm=0

Secondly, try putting =0d0 to force use of a real*8 zero, especially as you have used IMPLICIT NONE

Regards

Ian

Thanks for the tip in setting a whole array to a single value (although I was only using that as an example - I get the same results when actually trying to set the array elements to calculated values further down in the code).

I have tried using =0d0, but it makes no difference at all.

I have just tried compiling and debugging on an old compiler I have (which I cannot use commerically), and it sets all values to 0.0 as I thought it should, which suggests that the code is fine. I have also tried debugging on a 32 bit system rather than my standard 64 bit system, but again it does not make any difference at all, and I'm getting increasingly frustrated!

This code works OK for me but I have had to use my own input values.

The arrays A and U_NORM have sizes that require a back-handed calculation to get the sizes of the input arrays and this is probably where things are going wrong. The size (i.e. shape) of the two dimensional array A must match in the main program and the subroutine (strictly the first dimension only for a 2-D array).

The alternative is to use Fortran 90 assumed shape arrays.

You are asking for a lot of problems when defining the array dimension as you have. It may be legal fortran 90+, although I don't expect it is. Why use such a messy coding technique ?

REAL8 :: A(N_COMPS(MAX_PANS+1),TOT_PTS-N_COMPS) REAL8 :: U_NORM((MAX_PANS3)+N_COMPS)

My solution would be to transfer the dimensions in the argument list (fortran 77) or use implied array sizes, as Paul has suggested. If, as I suspect, the array A is not dimensioned as you imply in the calling routine, then calculate the dimensions before you call.

In the calling routine:- na1 = N_COMPS*(MAX_PANS+1) na2 = TOT_PTS-N_COMPS ! never negative ? nu = (MAX_PANS*3)+N_COMPS ! call SOLVER (N_COMPS, MAX_PANS, ALPHA, U, N_OUTER,
& VECT_POINTS_PERP, PANEL_VECTA, DIST_POINTS, A, V_PERP, VTAN, & GAMMA, N_PTS, TOT_PTS, na1, na2, nu)

In the routine SOLVER, use

REAL8 A(na1,na2) ! dummy argument REAL8 U_NORM(nu) ! local automatic array ?

! zero with A = 0 U_NORM = 0

should all work with all 90+ compilers.

You have checked any of the dimensions are -ve ? I'm sure that the array dimensions are of use elsewhere in the routines.