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Gluing graphs and the spectral gap: a Titchmarsh–Weyl matrix-valued function approach

Volume 255 / 2020

Pavel Kurasov, Sergei Naboko Studia Mathematica 255 (2020), 303-326 MSC: Primary 47A10; Secondary 35P25. DOI: 10.4064/sm190322-4-11 Published online: 4 May 2020


Assume that two metric graphs are joined by gluing a few vertices. We investigate the behaviour of the spectral gap for the corresponding standard Laplacians. It appears that a precise answer can be given in terms of the corresponding Titchmarsh–Weyl (matrix) functions of the two subgraphs, more precisely in terms of their negative spectral subspaces. We illustrate our results by considering explicit examples.


  • Pavel KurasovDepartment of Mathematics
    Stockholm University
    106 91 Stockholm, Sweden
  • Sergei NabokoDepartment of Mathematical Physics
    S:t Petersburg University
    198504 S:t Petersburg, Russia

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