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: "extended formulations for polygons"
  Abstract: The extension complexity of a polytope P is the smallest integer k such that P is the projection of a polytope Q with k facets. We study the extension complexity of n-gons in the plane. First, we give a new proof that the extension complexity of regular n-gons is O(logn), a result originating from work by Ben-Tal and Nemirovski (Math. Oper. Res. 26(2), 193–205, 2001). Our proof easily generalizes to other permutahedra and simplifies proofs of recent results by Goemans (2009), and Kaibel and Pashkovich (2011). Second, we prove a lower bound of $\sqrt{2n}$ on the extension complexity of generic n-gons. Finally, we prove that there exist n-gons whose vertices lie on an O(n)×O(n 2) integer grid with extension complexity $\varOmega (\sqrt{n}/\sqrt{\log n})$.

Connected through hyperedge HE-1 (induced by source paper "introduction to nonnegative matrix factorization"):
  with members:
    - "the non convex geometry of low rank matrix optimization"
    - "on the complexity of robust pca and l1 norm low rank matrix approximation"
    - "on restricted nonnegative matrix factorization"
    - "matrix completion has no spurious local minimum"
    - "low rank approximation with entrywise ell_1 norm error"
    - "input sparsity and hardness for robust subspace approximation"
    - "sketching as a tool for numerical linear algebra"
    - "the matching polytope has exponential extension complexity"

Connected through hyperedge HE-2 (induced by source paper "complexity of combinatorial optimization problems in terms of face lattices of associated polytopes"):
  with members:
    - "a special role of boolean quadratic polytopes among other combinatorial polytopes"
    - "the matching polytope has exponential extension complexity"

Connected through hyperedge HE-3 (induced by source paper "the matching polytope does not admit fully polynomial size relaxation schemes"):
  with members:
    - "average case polyhedral complexity of the maximum stable set problem"
    - "affine reductions for lps and sdps"
    - "lower bounds on the size of semidefinite programming relaxations"
    - "exponential lower bounds on the size of approximate formulations in the natural encoding for capacitated facility location"
    - "approximate constraint satisfaction requires large lp relaxations"
    - "on the existence of 0 1 polytopes with high semidefinite extension complexity"
    - "the matching polytope has exponential extension complexity"
    - "approximation limits of linear programs beyond hierarchies"

Connected through hyperedge HE-4 (induced by source paper "the matching polytope has exponential extension complexity"):
  with members:
    - "the matching polytope does not admit fully polynomial size relaxation schemes"
    - "lower bounds on the size of semidefinite programming relaxations"
    - "approximate constraint satisfaction requires large lp relaxations"
    - "on the existence of 0 1 polytopes with high semidefinite extension complexity"
    - "approximation limits of linear programs beyond hierarchies"
    - "extended formulations non negative factorizations and randomized communication protocols"

Connected through hyperedge HE-5 (induced by source paper "on the existence of 0 1 polytopes with high semidefinite extension complexity"):
  with members:
    - "the matching polytope has exponential extension complexity"
    - "approximation limits of linear programs beyond hierarchies"
    - "extended formulations non negative factorizations and randomized communication protocols"

Connected through hyperedge HE-6 (induced by source paper "a singly exponential time algorithm for computing nonnegative rank"):
  with members:
    - "computing a nonnegative matrix factorization provably"
    - "on the complexity of nonnegative matrix factorization"

Connected through hyperedge HE-7 (induced by source paper "computing a nonnegative matrix factorization provably"):
  with members:
    - "probabilistic latent semantic analysis"
    - "on the complexity of nonnegative matrix factorization"
    - "non negative matrix factorization with sparseness constraints"

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.DM(Discrete Mathematics)