Burago, D;    Ivanov, S;    Kurylev, Y;      (2014)    A graph discretization of the Laplace-Beltrami operator.                   Journal of Spectral Theory , 4  (4)   pp. 675-714.    10.4171/JST/83 <https://doi.org/10.4171/JST%2F83>.       Green open access