def __get_sigmas(self):
stack_sigma = {}<EOL>_stack = self.stack<EOL>_file_path = os.path.abspath(os.path.dirname(__file__))<EOL>_database_folder = os.path.join(_file_path, '<STR_LIT>', self.database)<EOL>_list_compounds = _stack.keys()<EOL>for _compound in _list_compounds:<EOL><INDENT>_list_element = _stack[_compound]['<STR_LIT>']<EOL>stack_sigma[_compound] = {}<EOL>for _element in _list_element:<EOL><INDENT>stack_sigma[_compound][_element] = {}<EOL>_list_isotopes = _stack[_compound][_element]['<STR_LIT>']['<STR_LIT:list>']<EOL>_list_file_names = _stack[_compound][_element]['<STR_LIT>']['<STR_LIT>']<EOL>_list_isotopic_ratio = _stack[_compound][_element]['<STR_LIT>']['<STR_LIT>']<EOL>_iso_file_ratio = zip(_list_isotopes, _list_file_names, _list_isotopic_ratio)<EOL>stack_sigma[_compound][_element]['<STR_LIT>'] = _list_isotopic_ratio<EOL>_sigma_all_isotopes = <NUM_LIT:0><EOL>_energy_all_isotpes = <NUM_LIT:0><EOL>for _iso, _file, _ratio in _iso_file_ratio:<EOL><INDENT>stack_sigma[_compound][_element][_iso] = {}<EOL>_file = os.path.join(_database_folder, _file)<EOL>_dict = _utilities.get_sigma(database_file_name=_file,<EOL>e_min=self.energy_min,<EOL>e_max=self.energy_max,<EOL>e_step=self.energy_step)<EOL>stack_sigma[_compound][_element][_iso]['<STR_LIT>'] = _dict['<STR_LIT>']<EOL>stack_sigma[_compound][_element][_iso]['<STR_LIT>'] = _dict['<STR_LIT>'] * _ratio<EOL>stack_sigma[_compound][_element][_iso]['<STR_LIT>'] = _dict['<STR_LIT>']<EOL>_sigma_all_isotopes += _dict['<STR_LIT>'] * _ratio<EOL>_energy_all_isotpes += _dict['<STR_LIT>']<EOL><DEDENT>_mean_energy_all_isotopes = _energy_all_isotpes / len(_list_isotopes)<EOL>stack_sigma[_compound][_element]['<STR_LIT>'] = _mean_energy_all_isotopes<EOL>stack_sigma[_compound][_element]['<STR_LIT>'] = _sigma_all_isotopes<EOL><DEDENT><DEDENT>self.stack_sigma = stack_sigma<EOL>
will populate the stack_sigma dictionary with the energy and sigma array
        for all the compound/element and isotopes