human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "on the design of nonlinear pid controller for nonlinear quadrotor system"
  Abstract: A nonlinear PID controller is proposed to stabilize the motion of a 6-DOF quadrotor and enforce it to track a given trajectory with minimum energy and error. We used the complete nonlinear model of the quadrotor in the design process, taking into account the velocity and acceleration vectors to keep the quadrotor model more accurate and close to the actual system. The asymptotic stability of the closed- loop system is proved using Lyapunov stability theorem under certain conditions. The simulations have been accomplished under MATLAB environment and included three different trajectories, i.e., circular, helical, and square. The proposed nonlinear PID controller has been compared with the linear PID one and the simulations showed the effectiveness of the proposed nonlinear PID controller in terms of speed, control energy, and steady-state error.

Connected through hyperedge HE-1 (induced by source paper "path planning of an autonomous mobile robot in a dynamic environment using modified bat swarm optimization"):
  with members:
    - "on the design of a novel finite time nonlinear extended state observer for class of nonlinear systems with mismatch disturbances and uncertainties"
    - "multi objective path planning of an autonomous mobile robot in static and dynamic environments using a hybrid pso mfb optimisation algorithm"

Connected through hyperedge HE-2 (induced by source paper "on the design of a novel finite time nonlinear extended state observer for class of nonlinear systems with mismatch disturbances and uncertainties"):
  with members:
    - "a novel second order nonlinear differentiator with application to active disturbance rejection control"
    - "an improved active disturbance rejection control for a differential drive mobile robot with mismatched disturbances and uncertainties"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.SY(Systems and Control)