docs: def set_objective(self, measured_metabolites):
          '''
          Updates objective function for given measured metabolites.
  
          :param dict measured_metabolites: dict in which keys are metabolite names 
              and values are float numbers represent fold changes in metabolites. 
          '''
          self.clean_objective()
          for k, v in measured_metabolites.items():
  
              m = self.model.metabolites.get_by_id(k)
              total_stoichiometry = m.total_stoichiometry(
                  self.without_transports)
  
              for r in m.producers(self.without_transports):
                  update_rate = v * r.metabolites[m] / total_stoichiometry
                  r.objective_coefficient += update_rate