A runtime error with Fortran formatting in MGDRAW user routine

Advanced Features and User Routines
1

Hello,

I am trying to run an exercise using the mgdraw user routine from a FLUKA advanced course. The goal is to prepare a phase-space file containing antiproton parameters for a subsequent simulation. The required logic is relatively simple, but I am encountering an issue with Fortran formatting.

When I try to write only the two variables JTRACK and ETRACK, the program works fine:

      ENTRY BXDRAW ( ICODE, MREG, NEWREG, XSCO, YSCO, ZSCO )

      if (lfirst) then
         call geon2r('ADTrgTi ', from_reg, ierr)
         call geon2r('ADTrgDs ', to_reg, ierr)
         OPEN(UNIT=99, FILE='aprots.txt', STATUS='UNKNOWN')
         lfirst = .false.
      end if

      if (MREG == from_reg .and. NEWREG == to_reg .and. JTRACK == 1) then
      write(99,'(I3,E15.7)') INT(JTRACK),SNGL(ETRACK)
      end if

      RETURN

but if I add any other variable to write, e.g. XTRACK:

      write(99,'(I3,2E15.7)') INT(JTRACK),SNGL(ETRACK),SNGL(XTRACK)
      end if

      RETURN

the program ends up with a runtime error:

At line 83 of file mgdraw_ex1.f (unit = 99, file = 'aprots.txt')
Fortran runtime error: Expected INTEGER for item 4 in formatted transfer, got REAL
(I3,2E15.7)
 ^

The error indicates that item #4 is expected to be an integer, even though there does not appear to be a fourth item.

Using * instead of '(I3,2E15.7)' also works, but then the output file is not written with the correct formatting.

Could you please suggest what I am doing wrong and why this error occurs?

I am not very experienced in Fortran programming so I am somewhat stuck.

FLUKA: 4-5.2
Flair: 3.4-5.3
Operating system: ubuntu 24.04 LTS

mgdraw_ex1.f (10.5 KB)

2

XTRACK is an array, containing at least two values (hence the 4th item), and not a single variable as ETRACK.
As a side note, you do not need to use INT(), since JTRACK is already an integer.

3

Hi @ceruttif,

Thank you! I completely overlooked that when I was reading through the slides and the trackr.inc file. I’ve made the changes now:

      write(99, '(I3,8E15.7)')
     & JTRACK, SNGL(ETRACK),
     & SNGL(XTRACK(I)), SNGL(YTRACK(I)),
     & SNGL(ZTRACK(I)), SNGL(CXTRCK),
     & SNGL(CYTRCK), SNGL(CZTRCK),
     & SNGL(WTRACK)

and everything works as expected!

4

Watch the value of the index I