Optimal Control Strategies for Multi-Agent Sheep Herding

TL;DR

This paper investigates optimal control methods for multi-agent sheep herding, comparing numerical techniques like solve_bvp, shooting, and iLQR, highlighting their limitations and scalability issues in complex, nonlinear multi-agent systems.

Contribution

It introduces a framework for modeling multi-agent herding with cost functionals and compares different numerical control strategies, emphasizing the advantages of iLQR in scalability.

Findings

iLQR outperforms shooting method in scalability

solve_bvp often fails to converge in high-dimensional systems

Nonlinearities cause oscillatory paths and slow convergence in control algorithms

Abstract

We develop a cost functional and state-space equations to model the problem of herding m sheep to the origin using n dogs. Our initial approach uses solve_bvp to approximate optimal control trajectories. But this method often fails to converge due to the system's high dimensionality and nonlinearity. However, with a well-chosen initial guess and carefully selected hyperparameters, we succeed in getting solve_bvp to converge. We also explore alternatives including the shooting method and linearization with the iterative Linear Quadratic Regulator (iLQR). While the shooting method also suffers from poor convergence, the linearized iLQR approach proves more scalable and successfully handles scenarios with more agents. However, it struggles in regions where dogs and sheep are in close proximity, due to strong nonlinearities that violate the assumptions of local linearization. This leads to jagged, oscillatory paths and slow convergence, particularly when the number of sheep exceeds the number of dogs. These challenges reveal key limitations of standard numerical techniques in multi-agent control and underscore the need for more robust, nonlinear strategies for coordinating interacting agents.