FUNCTION dustem_read_ext_lv,file,silent=silent

;=== determine the number of grains
str='                               '
OPENR,unit,file,/get_lun

;==read comments
str='' & first_char='#'
WHILE first_char EQ '#' DO BEGIN
  readf,unit,str
  first_char=strmid(str,0,1)
ENDWHILE
;readf,unit,str
CLOSE,unit
free_lun,unit
str=strcompress(str)
str=strtrim(str,2)
vv=str_sep(str,' ')
Ngrains=vv(0)

;Read model output
instruc='readcol,file,wav,'
FOR i=0L,Ngrains-1 DO BEGIN
  instruc=instruc+'abs_grain_'+strtrim(i+1,2)+','
ENDFOR
FOR i=0L,Ngrains-1 DO BEGIN
  instruc=instruc+'sca_grain_'+strtrim(i+1,2)+','
ENDFOR
;VG read ext_tot from the file
instruc=instruc+'ext_tot,silent=silent'
toto=execute(instruc)

;stop

;Nlines=n_elements(wav)-1
Nlines=n_elements(wav)

one_st = {wav:0., abs_grain:replicate(0.,Ngrains), sca_grain:replicate(0.,Ngrains),ext_tot:0.}
st=replicate(one_st,Nlines)

;VG : EXT.RES now contains the total absorption & scattering cross-sections per grain type in cm2/H 
;     no need for GRAIN.DAT to plot extinction anymore
;mH=1.66e-24
;fact=mH*1.e21

;st.wav=wav(1:*)
st.wav=wav

FOR iwav=0L,Nlines-1 DO BEGIN
   FOR igrain=0L,Ngrains-1 DO BEGIN
      instruc = 'st(iwav).abs_grain(igrain) = abs_grain_'+strtrim(igrain+1,2)+'(iwav)'
      toto = execute(instruc)
      instruc = 'st(iwav).sca_grain(igrain) = sca_grain_'+strtrim(igrain+1,2)+'(iwav)'
      toto = execute(instruc)
      ;st(iwav).ext_tot = st(iwav).ext_tot + fact * (st(iwav).abs_grain(igrain) + st(iwav).sca_grain(igrain))
      instruc = 'st(iwav).ext_tot = ext_tot(iwav)'
      toto = execute(instruc)
   ENDFOR
ENDFOR

return,st

END