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: "cost minimization of charging stations with photovoltaics an approach with ev classification"
  Abstract: This paper proposes a novel electric vehicle (EV) classification scheme for a photovoltaic (PV) powered EV charging station (CS) that reduces the effect of intermittency of electricity supply as well as reducing the cost of energy trading of the CS. Since not all EV drivers would like to be environmentally friendly, all vehicles in the CS are divided into three categories: 1) premium, 2) conservative, and 3) green, according to their charging behavior. Premium and conservative EVs are considered to be interested only in charging their batteries, with noticeably higher rate of charging for premium EVs. Green vehicles are more environmentally friendly, and thus assist the CS to reduce its cost of energy trading by allowing the CS to use their batteries as distributed storage. A different charging scheme is proposed for each type of EV, which is adopted by the CS to encourage more EVs to be green. A basic mixed integer programming (MIP) technique is used to facilitate the proposed classification scheme. It is shown that the uncertainty in PV generation can be effectively compensated, along with minimization of total cost of energy trading to the CS, by consolidating more green EVs. Real solar and pricing data are used for performance analysis of the system. It is demonstrated that the total cost to the CS reduces considerably as the percentage of green vehicles increases, and also that the contributions of green EVs in winter are greater than those in summer.

Connected through hyperedge HE-1 (induced by source paper "model predictive control for smart grids with multiple electric vehicle charging stations"):
  with members:
    - "load shifting in the smart grid to participate or not"
    - "a game theoretic approach to energy trading in the smart grid"

Connected through hyperedge HE-2 (induced by source paper "smart grid testbed for demand focused energy management in end user environments"):
  with members:
    - "design of a scalable hybrid mac protocol for heterogeneous m2m networks"
    - "prioritizing consumers in smart grid a game theoretic approach"
    - "three party energy management with distributed energy resources in smart grid"

Connected through hyperedge HE-3 (induced by source paper "management of renewable energy for a shared facility controller in smart grid"):
  with members:
    - "energy storage sharing in smart grid a modified auction based approach"
    - "price discrimination for energy trading in smart grid a game theoretic approach"
    - "three party energy management with distributed energy resources in smart grid"

Connected through hyperedge HE-4 (induced by source paper "distributed control for charging multiple electric vehicles with overload limitation"):
  with members:
    - "real time welfare maximizing regulation allocation in dynamic aggregator evs system"

Connected through hyperedge HE-5 (induced by source paper "price discrimination for energy trading in smart grid a game theoretic approach"):
  with members:
    - "customer engagement plans for peak load reduction in residential smart grids"
    - "prioritizing consumers in smart grid a game theoretic approach"
    - "three party energy management with distributed energy resources in smart grid"
    - "feasibility of using discriminate pricing schemes for energy trading in smart grid"
    - "a game theoretic approach to energy trading in the smart grid"
    - "distributed demand response and user adaptation in smart grids"

Connected through hyperedge HE-6 (induced by source paper "energy storage sharing in smart grid a modified auction based approach"):
  with members:
    - "customer engagement plans for peak load reduction in residential smart grids"
    - "price discrimination for energy trading in smart grid a game theoretic approach"
    - "prioritizing consumers in smart grid a game theoretic approach"
    - "three party energy management with distributed energy resources in smart grid"

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)