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: "on the stability of bubble functions and a stabilized mixed finite element formulation for the stokes problem"
  Abstract: In this paper we investigate the relationship between stabilized and enriched finite element formulations for the Stokes problem. We also present a new stabilized mixed formulation for which the stability parameter is derived purely by the method of weighted residuals. This new formulation allows equal-order interpolation for the velocity and pressure fields. Finally, we show by counterexample that a direct equivalence between subgrid-based stabilized finite element methods and Galerkin methods enriched by bubble functions cannot be constructed for quadrilateral and hexahedral elements using standard bubble functions. Copyright © 2008 John Wiley & Sons, Ltd.

Connected through hyperedge HE-1 (induced by source paper "modeling flow in porous media with double porosity permeability a stabilized mixed formulation error analysis and numerical solutions"):
  with members:
    - "mechanics based solution verification for porous media models"
    - "enforcing the non negativity constraint and maximum principles for diffusion with decay on general computational grids"
    - "dolfin automated finite element computing"
    - "a numerical study of fluids with pressure dependent viscosity flowing through a rigid porous medium"

Connected through hyperedge HE-2 (induced by source paper "a mixed formulation for a modification to darcy equation based on picard linearization and numerical solutions to large scale realistic problems"):
  with members:
    - "a numerical study of fluids with pressure dependent viscosity flowing through a rigid porous medium"

Connected through hyperedge HE-3 (induced by source paper "a mixed formulation for a modification to darcy equation with applications to enhanced oil recovery and carbon dioxide sequestration"):
  with members:
    - "a numerical study of fluids with pressure dependent viscosity flowing through a rigid porous medium"

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.NA(Numerical Analysis)