How to define two dimensional array in fortran - fortran

Question

I have catalog which I need to categorize its values in an array :
with this code
ii=1
101 read(20,*,end=102)ra(ii),dec(ii),mag_g(ii),mag_r(ii),mag_i(ii),redshift(ii)
do i=1,n
z(i)=zmin+(i-1)*step
zup(i)=z(i)+step
do j=1,b !mag loop
mag(j)=mag_min+(j-1)*bin
magup(j)=mag(j)+bin
if (z(i) >= redshift(ii).and.redshift(ii) <= zup(i).and.mag(j) >= mag_i(ii).and.mag_i(ii) <= magup(j) ) then
array(i,j)=mag_i(ii)
write(4,'(2x,3f10.5,2x,4f10.5)')z(i),zup(i),redshift(ii),mag(j),magup(j),mag_i(ii),array(i,j)
else
goto 103
end if
end do
end do
103 ii=ii+1
goto 101
102 total=ii-1
While I'm running this code, it overwrites all the values in each dimension.
How can define a two dimensional array with the rank of s, (all the objects fits in the if condition).
thanks

Answer 1

like Stefan said - you would need a 3D array. I see a couple of possible issues with your code:
Lines to long (I'm not sure gfortran would compile this with the default settings)
Gotos instead of loops
Unclear boundaries / dimensions
Not every element might be set
Order of the dimensions (Fortran is column major)
I would suggest something of the following if the number of elements (index ii) is known a priori:
! Allocate array
allocate( array( n, b, nElements ), stat=ierr )
if ( ierr .ne. 0 ) stop 'Cannot allocate memory!'
! Initialize array
array = 0
! Main loop
do ii=1,nElements
read(20,*,iostat=ierr)ra(ii),dec(ii),mag_g(ii),mag_r(ii),mag_i(ii),redshift(ii)
if ( ierr .ne. 0 ) stop 'Cannot read from unit 20!'
! Original loop
do i=1,n
z(i)=zmin+(i-1)*step
zup(i)=z(i)+step
do j=1,b !mag loop
mag(j)=mag_min+(j-1)*bin
magup(j)=mag(j)+bin
if (z(i) >= redshift(ii) .and.&
redshift(ii) <= zup(i).and. &
mag(j) >= mag_i(ii).and. &
mag_i(ii) <= magup(j) ) then
! Write value
array(i,j,ii)=mag_i(ii)
write(4,'(2x,3f10.5,2x,4f10.5)') z(i),zup(i),redshift(ii), &
mag(j),magup(j),mag_i(ii),array(i,j,ii)
end if
end do ! j
end do ! i
enddo ! ii
! [...]
! Clean up
if ( allocated(array) ) deallocate(array)
Of course, this is Fortran 90/95 so you would need to convert this to Fortran 77 if necessary.
If the number of elements is not known, you could either use chained lists (which might be oversized depending on the problem), or define an upper limit and use the code above. Then, you need to change the stop statement within the loop to an exit statement and store the actual number of elements.
If you are dealing with large arrays I would strongly suggest to change the order of the dimensions:
! Allocate array
allocate( array( b, n, nElements ), stat=ierr )
if ( ierr .ne. 0 ) stop 'Cannot allocate memory!'
! [...]
array(j,i,ii) = mag_i(ii)