  This paper addresses the problem of positive consensus of directed
multi-agent systems with observer-type output-feedback protocols. More
specifically, directed graph is used to model the communication topology of the
multi-agent system and linear matrix inequalities (LMIs) are used in the
consensus analysis in this paper. Using positive systems theory and graph
theory, a convex programming algorithm is developed to design appropriate
protocols such that the multi-agent system is able to reach consensus with its
state trajectory always remaining in the non-negative orthant. Finally,
numerical simulations are given to illustrate the effectiveness of the derived
theoretical results.
