%------------------------------------------------------------------------
% NAME:     qp_x2arts
%
%           Maps a state vector to ARTS variables or to a correction term
%           for the measured spectrum.
%
%           The function can be used for iterative retrievals to apply the
%           present state.
%
%           Atmospheric variables are maped to ARTS, while sensor variables
%           are maped to a correction term for the spectrum. The correction
%           term can include for example fit of baseline ripple. This term
%           shall be subtracted from the measurement spectrum.
%
%           If the RECALC_ABS=0, the absorption is scaled to match the
%           retrieved species profiles. If RECALC_ABS=1, only the species
%           profiles are stored and the absorption must be recalculed in
%           next iteration.
%
%           The function is developed for qpcls but can maybe be useful
%           for other purposes.
%
% FORMAT:   yc = map_x( x, basename, Kx, kx_names, kx_index, kx_aux, 
%                          recalc_abs, logspecies, p_abs, vmrs, Abs, Absp, za )
%
% OUT:      yc          Correction term for measurement spectrum.
% IN:       basename    Basename for the ARTS calculations.
%           Kx          Weighting function matrix.
%           kx_names    As the corresponding ARTS variable.
%           kx_index    Start and stop index for each retrieval identity.
%                       A 2 column matrix.
%           kx_aux      As the corresponding ARTS variable.
%           recalc_abs  Flag to determine if absorption will be recalculated
%           logspecies  Flag for retrieval of the log. of species.
%           p_abs       As ARTS variable p_abs.
%           vmrs        As ARTS variable vmrs.
%           Abs         As ARTS variable abs.
%           Absp        As ARTS variable abs_per_tg.
%           za          As ARTS variable za_pencil.
%------------------------------------------------------------------------

% HISTORY: 2001.01.04  Started by by Patrick Eriksson.


function yc = map_x( x, basename, Kx, kx_names, kx_index, kx_aux, recalc_abs, logspecies, p_abs, vmrs, Abs, Absp, za )


yc       = 0;
ispecies = 0;
nf       = size( Abs, 1 );


for i = 1:size(kx_names,1)

  [group,name,par1] = qp_kinfo( kx_names{i} );

  ind = kx_index(i,1):kx_index(i,2);

  %=== Species
  %
  if strcmp( group, 'Species' )
    %
    ispecies = ispecies + 1;
    %
    xp = interpp( kx_aux(ind,1), x(ind), p_abs );
    %
    if logspecies
      xp = exp( xp );
    end
    %
    vmrs(ispecies,:) = vmrs(ispecies,:) .* xp'; 
    %
    if ~recalc_abs
      %
      dAbs = Absp{ispecies} .* ( ones(nf,1) * (xp-1)' );
      Absp{ispecies} = Absp{ispecies} + dAbs; 
      Abs = Abs + dAbs;
      %
    end


  %=== Temperature
  %
  elseif strcmp( group, 'Temperature' )
    %
    t_abs = interpp( kx_aux(ind,1), x(ind), p_abs );
    write_artsvar( basename, 't_abs', t_abs, 'b' );


  %=== Pointing off-set
  %
  elseif strcmp( name, 'Pointing: off-set' )
    %
    za = za + x(ind);
    write_artsvar( basename, 'za_pencil', za, 'b' );


  %=== Polynomial baseline fits
  %
  elseif strncmp( group, 'Baseline', 8 )
    %
    yc = yc + Kx(:,ind) * x(ind);
    

  else
     error(sprintf( 'Unknown retrieval identity: %s', name ));
  end
end


%=== Save profile/absorption data
%
write_artsvar( basename, 'vmrs', vmrs, 'b' );
%
if ~recalc_abs
  write_artsvar( basename, 'abs', Abs, 'b' );
  write_artsvar( basename, 'abs_per_tg', Absp, 'b' );
end