Wrong filling matrix in Fortran

Question

I have the following problem:

I have a subroutine on Fortran 77, which must return a one-dimensional array, D_Y. All values which are needed are transferred correctly from the main program, but three elements of the matrix D_Y (D_Y(16-18)) are set to 0.0 and I don't know why.

NDIM=18, P1 and P2 are right, all parameters, which they have in equation are right too, but their sum is always set to 0!

SUBROUTINE DY(Y,T,PARAM,NDIM,D_Y)
  IMPLICIT NONE
    real(8),intent(in)::Y(*)
    real(8),intent(in)::PARAM(*),T
  real(8),intent(out)::D_Y(NDIM)
  integer::D
  integer,intent(in)::NDIM
    real(8)::R,R1,R2,P1,P2
  open(18,file='kinetic2.txt',status='unknown')

  R=((Y(1)-Y(4))**2.D0+(Y(2)-Y(5))**2.D0+(Y(3)-Y(6))**2.D0)**0.5D0
  R1=((Y(1)-Y(13))**2.D0+(Y(2)-Y(14))**2.D0+(Y(3)-Y(15))**2.D0)**0.5D0
  R2=((Y(4)-Y(13))**2.D0+(Y(5)-Y(14))**2.D0+(Y(6)-Y(15))**2.D0)**0.5D0

 DO D=1,6
  D_Y(D)=Y(D+6)
 END DO

 DO D=7,9
  D_Y(D)=-(PARAM(1)*PARAM(3))*(Y(D-6)-Y(D-3))/((R)**3.D0)
 END DO

 DO D=10,12
  D_Y(D)=-(PARAM(1)*PARAM(2))*(Y(D-6)-Y(D-9))/((R)**3.D0)
 END DO

 DO D=13,15
  D_Y(D)=Y(D+3)
 END DO

 DO D=16,18
  P1=-(PARAM(1)*PARAM(3))*(Y(D-3)-Y(D-12))/((R2)**3.D0)
  P2=-(PARAM(1)*PARAM(2))*(Y(D-3)-Y(D-15))/((R1)**3.D0)
D_Y(D)=P1+P2
            write(18,*) P1,P2,D_Y(D)
 END DO
  RETURN
  END

Answer 1

If your compiler is treating your code as fixed form a D in column 1, such as in the line

D_Y(D)=P1+P2

may be understood to be a comment. Check your compiler documentation and options.