n this section we compute the spectrum of the Laplacian
explicitly. It will be seen that the Gershgorin theorem gives a good boundary.
We introduce the lattice
and consider the spectral
problem
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(Laplace problem)
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(Laplace bounds)
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We introduce the lattice functions
with the
values
Such functions satisfy the boundary conditions
(
Laplace bounds
) and constitute a basis in
linear algebra sense. We compute action of the operator
on
:
Since
we have
Therefore,
are eigenvalues and
constitute the spectrum of
:
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(Laplacian Spectrum)
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We have the spectral
limits
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(Laplacian Limits)
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