public void print_as_matrix(){
        for(Node line : nodes.values()){
            for(Node column : nodes.values()){
                Edge e = null;
                for(Edge f : edges.values()){
                    if(f.from() == line && f.to() == column){
                        e = f;
                        break;
                    }
                }
                if(e == null){
                    System.out.print("0/0 ");
                }
                else {
                    System.out.print(e.get_capacity()+"/"+e.get_flow()+ " ");
                }
            }
            System.out.print("\n");
        }
    }