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: "the optimal placement delivery arrays"
  Abstract: In wireless networks, coded caching is an effective technique to reduce network congestion during peak traffic times. Recently, a new concept called placement delivery array (PDA) was proposed to characterize the coded caching scheme. So far, only one class of PDAs by Maddah-Ali and Niesen is known to be optimal. In this paper, we mainly focus on constructing optimal PDAs. Firstly, we derive some lower bounds. Next, we present several infinite classes of PDAs, which are shown to be optimal with respect to the new bounds.

Connected through hyperedge HE-1 (induced by source paper "optimal placement delivery arrays with minimum number of rows"):
  with members:
    - "on the placement delivery array design for centralized coded caching scheme"
    - "coded caching with linear subpacketization is possible using ruzsa szem eredi graphs"
    - "a new converse bound for coded caching"
    - "coded caching with low subpacketization levels"
    - "fundamental limits of caching improved delivery rate cache capacity trade off"
    - "wireless content caching for small cell and d2d networks"
    - "caching and delivery via interference elimination"
    - "on the optimality of uncoded cache placement"

Connected through hyperedge HE-2 (induced by source paper "some new bounds of placement delivery arrays"):
  with members:
    - "placement delivery array design through strong edge coloring of bipartite graphs"
    - "optimal placement delivery arrays with minimum number of rows"
    - "a new converse bound for coded caching"
    - "fundamental limits of caching improved delivery rate cache capacity trade off"
    - "centralized coded caching schemes a hypergraph theoretical approach"
    - "new results for traitor tracing schemes"
    - "a note on the fundamental limits of coded caching"
    - "hierarchical coded caching"

Connected through hyperedge HE-3 (induced by source paper "a novel recursive construction for coded caching schemes"):
  with members:
    - "placement delivery array design through strong edge coloring of bipartite graphs"
    - "optimal placement delivery arrays with minimum number of rows"
    - "on the placement delivery array design for centralized coded caching scheme"
    - "coded caching schemes with reduced subpacketization from linear block codes"
    - "coded caching with low subpacketization levels"
    - "wireless content caching for small cell and d2d networks"
    - "hierarchical coded caching"
    - "fundamental limits of caching in wireless d2d networks"

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.IT(Information Theory)