  In this paper, we address two forms of consensus for multi-agent systems with
undirected, signed, weighted, and connected communication graphs, under the
assumption that the agents can be partitioned into three clusters, representing
the decision classes on a given specific topic, for instance, the in favour,
abstained and opponent agents. We will show that under some assumptions on the
cooperative/antagonistic relationships among the agents, simple modifications
of DeGroot's algorithm allow to achieve tripartite consensus(if the opinions of
agents belonging to the same class all converge to the same decision) or sign
consensus (if the opinions of the agents in the three clusters converge to
positive, zero and negative values, respectively).
