code: def is_consistent(database, solver, exchange=set(), zeromass=set()):
      
  
      prob = solver.create_problem()
      compound_set = _non_localized_compounds(database)
      mass_compounds = compound_set.difference(zeromass)
  
      # Define mass variables
      m = prob.namespace(mass_compounds, lower=1)
      prob.set_objective(m.sum(mass_compounds))
  
      # Define constraints
      massbalance_lhs = {reaction: 0 for reaction in database.reactions}
      for (compound, reaction), value in iteritems(database.matrix):
          if compound not in zeromass:
              mass = m(compound.in_compartment(None))
              massbalance_lhs[reaction] += mass * value
      for reaction, lhs in iteritems(massbalance_lhs):
          if reaction not in exchange:
              prob.add_linear_constraints(lhs == 0)
  
      result = prob.solve_unchecked(lp.ObjectiveSense.Minimize)
      return result.success
docs: Try to assign a positive mass to each compound
  
      Return True if successful. The masses are simply constrained by m_i > 1 and
      finding a solution under these conditions proves that the database is mass
      consistent.