Consensus problems for the case that part of members without using private state information in a multi-agent
system are studied. A new consensus protocol is given with the properties that not all the agents, even none of them need to
use their private state information. Based on the matrix theory and graph theory, it is proved that consensus problems can
be solved for both fixed and switching topology by studying the structure of graphs corresponding to nonnegative matrices.
If and only if the root vertex has a loop in the interaction topology which has a spanning tree, then the system can achieve
consensus asymptotically. Simulations results show the correctness of theoretical conclusion..