PRO dustem_write_lambda,file,st,help=help

;+
; NAME:
;   dustem_write_lambda
;
; PURPOSE:
;   writes information relating to wavelength grid
;   corresponding .DAT file
;
; CATEGORY:
;    DustEMWrap, Distributed, LowLevel, Initialization
;
; CALLING SEQUENCE:
;   dustem_write_lambda,file,st
;
; INPUTS:
;    st   : dustem data structure
;    file  : output file to be written
;
; OPTIONAL INPUT PARAMETERS:
;    None
;
; OUTPUTS:
;    None
;
; OPTIONAL OUTPUT PARAMETERS:
;    None
;
; ACCEPTED KEY-WORDS:
;    help     : writes this help
;
; COMMON BLOCKS:
;    None
;
; SIDE EFFECTS:
;    Files are written
;
; RESTRICTIONS:
;    The DustEM fortran code must be installed
;    The DustEMWrap IDL code must be installed
;
; PROCEDURES AND SUBROUTINES USED:  
;
; EXAMPLES:
;
; MODIFICATION HISTORY:
;    Evolution details on the DustEMWrap gitlab.
;    See http://dustemwrap.irap.omp.eu/ for FAQ and help.  
;-
  
  IF keyword_set(help) THEN BEGIN
     doc_library,'dustem_write_lambda'
     goto,the_end
  ENDIF

  
;stop
openw,unit,file,/get_lun

Nwaves=n_elements(st)
printf,unit,fix(st(0).lambda)

FOR i=1L,Nwaves-1 DO BEGIN
  printf,unit,st(i).lambda,format=frmt
ENDFOR

close,unit
free_lun,unit

the_end:
END