pref_ind = 1; % level of reference pressure for the HSE
zref_ind = 1; % level of reference pressure for the HSE

% call structure 
Q=qpack('spectro_sample')
  %create the retrieval grid, This is just to have a consistent
  %retrieval grid even the atmosphere setup is changed
     grid.lowstrato = [2:2:30]*1e3; 
     grid_2km = [2:2:60]*1e3;
     grid_3km = [2:3:60]*1e3;
     grid_4km = [2:4:60]*1e3;
    % read into the pressure profile
     PTZ_FILE = Q.APRIORI_PTZ;  
      ptz=read_datafile(PTZ_FILE, 'Matrix');
     % find the corresponding values for pref and zref necessary
     % for hydrostatic calculation.ptz=read_datafile(PTZ_FILE, 'Matrix');     
     pref = ptz(pref_ind, 1);
     zref = ptz(pref_ind, 3);
     p_abs=loggrid([ptz(1,1),ptz(size(ptz,1), 1)], 15); 
     
     % create the grid in pressure units
     grid.lowstrato=interp1(ptz(:,3), ptz(:,1), grid.lowstrato );
     grid_2km=interp1(ptz(:,3), ptz(:,1), grid_2km );
     grid_3km=interp1(ptz(:,3), ptz(:,1), grid_3km );
     grid_4km=interp1(ptz(:,3), ptz(:,1), grid_4km );
     %
     % write into the files 
     write_datafile([Q.CALCGRIDS_DIR,'/p_abs.aa'], p_abs,...
         'Vector');
     write_datafile([Q.RETRIEVDEF_DIR,'/grid.lowstrato.aa'], grid.lowstrato, ...
         'Vector');
     write_datafile([Q.RETRIEVDEF_DIR,'/grid_2km.aa'], grid_2km, ...
         'Vector');
     write_datafile([Q.RETRIEVDEF_DIR,'/grid_3km.aa'], grid_3km, ...
         'Vector');
     write_datafile([Q.RETRIEVDEF_DIR,'/grid_4km.aa'], grid_4km, ...
         'Vector');       
     
     Q.HSE_PREF = ptz(pref_ind, 1);
     Q.HSE_ZREF = ptz(pref_ind, 3);

    qp_H(Q); 
    qp_Se(Q);
    qp_Sx(Q);
    qpcls_invchar(Q);