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: "robot impedance control and passivity analysis with inner torque and velocity feedback loops"
  Abstract: Impedance control is a well-established technique to control interaction forces in robotics. However, real implementations of impedance control with an inner loop may suffer from several limitations. In particular, the viable range of stable stiffness and damping values can be strongly affected by the bandwidth of the inner control loops (e.g., a torque loop) as well as by the filtering and sampling frequency. This paper provides an extensive analysis on how these aspects influence the stability region of impedance parameters as well as the passivity of the system. This will be supported by both simulations and experimental data. Moreover, a methodology for designing joint impedance controllers based on an inner torque loop and a positive velocity feedback loop will be presented. The goal of the velocity feedback is to increase (given the constraints to preserve stability) the bandwidth of the torque loop without the need of a complex controller.

Connected through hyperedge HE-1 (induced by source paper "stance locomotion adaptation over soft terrain"):
  with members:
    - "heuristic planning for rough terrain locomotion in presence of external disturbances and variable perception quality"
    - "frequency aware model predictive control"
    - "dynamic locomotion for passive ankle biped robots and humanoids using whole body locomotion control"
    - "passive whole body control for quadruped robots experimental validation over challenging terrain"
    - "contact implicit optimization of locomotion trajectories for a quadrupedal microrobot"
    - "whole body nonlinear model predictive control through contacts for quadrupeds"
    - "robust whole body motion control of legged robots"
    - "momentum control with hierarchical inverse dynamics on a torque controlled humanoid"

Connected through hyperedge HE-2 (induced by source paper "feedback mpc for torque controlled legged robots"):
  with members:
    - "sensitivity of legged balance control to uncertainties and sampling period"
    - "frequency aware model predictive control"
    - "real time motion planning of legged robots a model predictive control approach"
    - "an efficient optimal planning and control framework for quadrupedal locomotion"
    - "balancing and walking using full dynamics lqr control with contact constraints"

Connected through hyperedge HE-3 (induced by source paper "safe rendering of high impedance on a series elastic actuator with disturbance observer based torque control"):
  with members:
    - "necessary and sufficient conditions for passivity of velocity sourced impedance control of series elastic actuators"
    - "bounded collision force by the sobolev norm compliance and control for interactive robots"

Connected through hyperedge HE-4 (induced by source paper "distributed impedance control of latency prone robotic systems with series elastic actuation"):
  with members:
    - "controlit a software framework for whole body operational space control"

Connected through hyperedge HE-5 (induced by source paper "a planning and control framework for humanoid systems robust optimal and real time performance"):
  with members:
    - "momentum control with hierarchical inverse dynamics on a torque controlled humanoid"
    - "funnel libraries for real time robust feedback motion planning"
    - "a framework for planning and controlling non periodic bipedal locomotion"
    - "stability and performance limits of latency prone distributed feedback controllers"
    - "full body collision detection and reaction with omnidirectional mobile platforms a step towards safe human robot interaction"
    - "controlit a software framework for whole body operational space control"
    - "zmp support areas for multi contact mobility under frictional constraints"
    - "real time planning with primitives for dynamic walking over uneven terrain"

Connected through hyperedge HE-6 (induced by source paper "balancing and walking using full dynamics lqr control with contact constraints"):
  with members:
    - "risk sensitive nonlinear optimal control with measurement uncertainty"
    - "inertial sensor based humanoid joint state estimation"
    - "balancing experiments on a torque controlled humanoid with hierarchical inverse dynamics"

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)