Are the eigenvalues of the B-spline isogeometric analysis approximation of -Δu = λu known in almost closed form?

Sven-Erik Ekström, Isabella Furci, Carlo Garoni, Carla Manni, Stefano Serra Capizzano, Hendrik Speleers. Are the eigenvalues of the B-spline isogeometric analysis approximation of -Δu = λu known in almost closed form?. Numerical Lin. Alg. with Applic., 25(5), 2018. [doi]

@article{EkstromFGMCS18,
  title = {Are the eigenvalues of the B-spline isogeometric analysis approximation of -Δu = λu known in almost closed form?},
  author = {Sven-Erik Ekström and Isabella Furci and Carlo Garoni and Carla Manni and Stefano Serra Capizzano and Hendrik Speleers},
  year = {2018},
  doi = {10.1002/nla.2198},
  url = {https://doi.org/10.1002/nla.2198},
  researchr = {https://researchr.org/publication/EkstromFGMCS18},
  cites = {0},
  citedby = {0},
  journal = {Numerical Lin. Alg. with Applic.},
  volume = {25},
  number = {5},
}