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: "improved girth approximation and roundtrip spanners"
  Abstract: In this paper we provide improved algorithms for approximating the girth and producing roundtrip spanners of $n$-node $m$-edge directed graphs with non-negative edge lengths. First, for any integer $k \ge 1$, we provide a deterministic $\tilde{O}(m^{1+ 1/k})$ time algorithm which computes a $O(k\log\log n)$ multiplicative approximation of the girth and a $O(k\log\log n)$ multiplicative roundtrip spanner with $\tilde{O}(n^{1+1/k})$ edges. Second, we provide a randomized $\tilde{O}(m\sqrt{n})$ time algorithm that with high probability computes a 3-multiplicative approximation to the girth. Third, we show how to combine these algorithms to obtain for any integer $k \ge 1$ a randomized algorithm which in $\tilde{O}(m^{1+ 1/k})$ time computes a $O(k\log k)$ multiplicative approximation of the girth and $O(k \log k)$ multiplicative roundtrip spanner with high probability. #R##N#The previous fastest algorithms for these problems either ran in All-Pairs Shortest Paths (APSP) time, i.e. $\tilde{O}(mn)$, or were due Pachocki et al (SODA 2018) which provided a randomized algorithm that for any integer $k \ge 1$ in time $\tilde{O}(m^{1+1/k})$ computed with high probability a $O(k\log n)$ multiplicative approximation of the girth and a $O(k\log n)$ multiplicative roundtrip spanners with $\tilde{O}(n^{1+1/k})$ edges. Our first algorithm removes the need for randomness and improves the approximation factor in Pachocki et al (SODA 2018), our second is constitutes the first sub-APSP-time algorithm for approximating the girth to constant accuracy with high probability, and our third is the first time versus quality trade-offs for obtaining constant approximations.

Connected through hyperedge HE-1 (induced by source paper "roundtrip spanners with 2k 1 stretch"):
  with members:
    - "approximating cycles in directed graphs fast algorithms for girth and roundtrip spanners"
    - "directed spanners via flow based linear programs"

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.DS(Data Structures and Algorithms)