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

subroutine locate_element (ring, str, loc, err_flag)

  use cesrv_struct
  use cesrv_interface

  implicit none

  type (lat_struct) ring
  integer loc, i, ix
  character :: str*(*), digits*10 = '0123456789'
  logical err_flag, is_number

! trim leading blanks

  call string_trim (str, str, ix)
  if (ix == 0) then
    print *, 'ERROR IN LOCATE_ELEMENT: NO ELEMENT NAME GIVEN.'
    err_flag = .true.
    return
  endif

! string may be a number (the index of the element) or an element's name.

  is_number = .true.

  do i = 1, ix
    if (index(digits, str(i:i)) == 0) is_number = .false.
  enddo

!

  err_flag = .false.   ! assume everything is OK

  if (is_number) then
    read (str, *) loc
    if (loc < 0 .or. loc > ring%n_ele_max) then
      print *, 'ERROR IN LOCATE_ELEMENT: RING INDEX OUT OF RANGE: ', str
      err_flag = .true.
    endif
    return
  endif

! here if str is an element's name.

  do loc = 1, ring%n_ele_max
    if (ring%ele(loc)%name == str(:ix)) return
  enddo

  print *, 'ERROR IN LOCATE_ELEMENT: CANNOT MATCH ELEMENT NAME: ', str(:ix)
  print *, '       WITH ANY ELEMENT IN THE RING.'
  err_flag = .true.

end subroutine