FUNCTION dustem_plugin_modify_dust_pol, st, key=key, val=val, scope=scope, paramtag=paramtag, help=help

;+
; NAME:
;    dustem_plugin_modify_dust_pol
; PURPOSE:

;    modifies stokes Q,U values for dust polarization in st according to the given keywords and values

; CATEGORY:
;    DUSTEM Wrapper
; CALLING SEQUENCE:

;    a=dustem_plugin_modify_dust_pol(st,[key=][val=][,scope=][,paramtag=][,/help])

; INPUTS:

;    st = dustem structure

; OPTIONAL INPUT PARAMETERS:

;    key  = input parameter numbers (first = polarization fraction in %, default=1.%, second=polarization angle, default=0.)
;    val  = input parameter values

; OUTPUTS:
;    out = array containing the stokes emission parameters associated to the dust/synchrotron component or a concatenated version for both
; OPTIONAL OUTPUT PARAMETERS:

;    scope = if set, returns only the scope of the pluggin
;    paramtag = if set, returns only the parameter tags

; ACCEPTED KEY-WORDS:
;    help                  = if set, print this help
; COMMON BLOCKS:
;    None
; SIDE EFFECTS:
;    None
; RESTRICTIONS:
;    The dustem fortran code must be installed
;    The dustem idl wrapper must be installed
; PROCEDURE:
;    This is a dustem plugin
;-

IF keyword_set(help) THEN BEGIN

  doc_library,'dustem_plugin_modify_dust_pol'

  out=0.

  GOTO,the_end

ENDIF

IF not keyword_set(set) THEN BEGIN
    
    st=*!dustem_current

ENDIF

IF keyword_set(scope) THEN BEGIN
    out=0.

    GOTO, the_scope

ENDIF 

IF keyword_set(paramtag) THEN BEGIN
    out=0.

    GOTO, the_paramtag

ENDIF 

;below are the default values for the plugin parameters

smallp_fact=1.     ;This is the default multiplicative factore to the dust polarization
psi=0.             ;This is the default polarization angle

IF keyword_set(key) THEN BEGIN 
  ind1=where(key EQ 1,count1)
  ind2=where(key EQ 2,count2)

  IF count1 NE 0 THEN smallp_fact=val[ind1[0]] ; setting smallp from pd - this is another polarization fraction (constant) that is applied to the total dust emission

  IF count2 NE 0 THEN psi=val[ind2[0]] & !dustem_psi = psi ; setting psi from pd.  !dustem_psi here helps for the plotting.   

ENDIF

fact = 1.e4*(*!dustem_HCD)/(4.*!pi)/(3.e8/1.e-6/((st.polsed).wav))*1.e20/1.e7

P=((st.polsed).em_tot)*fact   ; This is the polarized emission P
I=((st.sed).em_tot)*fact      ; This is the total intensity emission I

Nwaves=(size(I))[1]

frac_model=P/I    ;This is the polarization fraction in the model

frac_used=frac_model*smallp_fact

psi_used = replicate(psi,Nwaves)

polar_ippsi2iqu,I,Q,U,frac_used,psi_used

out=fltarr(Nwaves,3) ; modified this. This is the only plugin that has this number of outputs.

;degtorad = !pi/180

out[*,0]=I
out[*,1]=Q
out[*,2]=U

; out[*,3]=frac_used
; ;out[*,4]=0.5*atan(U,Q)/degtorad
; out[*,4]=psi_used

the_scope:

scope='REPLACE_POLSED'

the_paramtag:
paramtag=['p','Psi (deg)']

RETURN, out

the_end:

END