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A discrete Gauss-Green identity for unbounded Laplace operators, and the transience of random walks
Journal article   Peer reviewed

A discrete Gauss-Green identity for unbounded Laplace operators, and the transience of random walks

Palle Jorgensen and Erin Pearse
Israel Journal of Mathematics, Vol.196(1), pp.113-160
08/2013
DOI: 10.1007/s11856-012-0165-2

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Abstract

On a finite network (connected weighted undirected graph), the relationship between the natural Dirichlet form E and the discrete Laplace operator Δ is given by $$\varepsilon (u,v) = {\langle u,\Delta v\rangle _{{\ell ^2}}}$$ , where the latter is the usual ℓ 2 inner product. This formula is not generally true for infinite networks; earlier authors have given various conditions under which this formula remains valid. Instead, we extend this formula to arbitrary infinite networks (including the case when Δ is unbounded) by including a new (boundary) term, in parallel with the classical Gauss-Green identity. This tool allows for detailed study of the boundary of the network. We construct a reproducing kernel for the space of functions of finite energy which allows us to specify a dense domain for Δ and give several criteria for the transience of the random walk on the network. The extended Gauss-Green identity and the reproducing kernel also yield a boundary integral representation for harmonic functions of finite energy. The boundary representation is developed further in [24].
Algebra Analysis Theoretical, Mathematical and Computational Physics Mathematics, general Mathematics Group Theory and Generalizations Applications of Mathematics

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