Multi-agent coordination control usually involves a potential function that encodes information of a global control task, while the control input for individual agents is often designed by a gradient-based control law. The property of Hessian matrix associated with a potential function plays an important role in the stability analysis of equilibrium points in gradient-based coordination control systems. Therefore, the identification of Hessian matrix in gradient-based multi-agent coordination systems becomes a key step in multi-agent equilibrium analysis. However, very often the identification of Hessian matrix via the entry-wise calculation is a very tedious task and can easily introduce calculation errors. In this paper we present some general and fast approaches for the identification of Hessian matrix based on matrix differentials and calculus rules, which can easily derive a compact form of Hessian matrix for multi-agent coordination systems. We also present several examples on Hessian identification for certain typical potential functions involving edge-tension distance functions and triangular-area functions, and illustrate their applications in the context of distributed coordination and formation control.1 taken into consideration in the Hessian formula. The standard way of Hessian identification usually involves entrywise calculation, which we refer as 'direct' approach. But this approach soon becomes intractable when a multi-agent coordination system under consideration involves complicated dynamics, and the interaction graph grows in size with more complex topologies. Alternatively, matrix calculus that takes into account graph topology and coordination laws can offer a more convenient approach in identifying Hessian matrices and deriving a compact Hessian formula, and this motivates this paper.In this paper, with the help of matrix differentials and calculus rules, we discuss Hessian identification for several typical potentials commonly-used in gradient-based multi-agent coordination control. We do not aim to provide a comprehensive study on Hessian identification for multi-agent coordination systems, but we will identify Hessian matrices for two general potentials associated with an underlying undirected graph topology. The first is an edgebased, distance-constrained potential that is defined by an edge function for a pair of agents, usually involving inter-agent distances. The overall potential is a sum of all individual potentials over all edges. The second type of potential function is defined by a three-agent subgraph, usually involving the (signed) area quantity spanned by a three-agent subgraph. We will use the formation control with signed area constraints as an example of such distributed coordination systems, and illustrate how to derive Hessian matrix for these coordination potentials in a general graph. The identification process of Hessian formula can be extended in identifying other Hessians matrices in even more general potential functions used in multi-agent coordination control.
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