24 research outputs found
A Cheeger-Buser-Type inequality on CW complexes
We extend the definition of boundary expansion to CW complexes and prove a
Cheeger-Buser-Type relation between the spectral gap of the Laplacian and the
expansion of an orientable CW complex
High Dimensional Expanders and Property Testing
We show that the high dimensional expansion property as defined by Gromov,
Linial and Meshulam, for simplicial complexes is a form of testability. Namely,
a simplicial complex is a high dimensional expander iff a suitable property is
testable. Using this connection, we derive several testability results
Higher Dimensional Discrete Cheeger Inequalities
For graphs there exists a strong connection between spectral and
combinatorial expansion properties. This is expressed, e.g., by the discrete
Cheeger inequality, the lower bound of which states that , where is the second smallest eigenvalue of the Laplacian of
a graph and is the Cheeger constant measuring the edge expansion of
. We are interested in generalizations of expansion properties to finite
simplicial complexes of higher dimension (or uniform hypergraphs).
Whereas higher dimensional Laplacians were introduced already in 1945 by
Eckmann, the generalization of edge expansion to simplicial complexes is not
straightforward. Recently, a topologically motivated notion analogous to edge
expansion that is based on -cohomology was introduced by Gromov
and independently by Linial, Meshulam and Wallach. It is known that for this
generalization there is no higher dimensional analogue of the lower bound of
the Cheeger inequality. A different, combinatorially motivated generalization
of the Cheeger constant, denoted by , was studied by Parzanchevski,
Rosenthal and Tessler. They showed that indeed , where
is the smallest non-trivial eigenvalue of the (-dimensional
upper) Laplacian, for the case of -dimensional simplicial complexes with
complete -skeleton.
Whether this inequality also holds for -dimensional complexes with
non-complete -skeleton has been an open question. We give two proofs of
the inequality for arbitrary complexes. The proofs differ strongly in the
methods and structures employed, and each allows for a different kind of
additional strengthening of the original result.Comment: 14 pages, 2 figure
Topology of random simplicial complexes: a survey
This expository article is based on a lecture from the Stanford Symposium on
Algebraic Topology: Application and New Directions, held in honor of Gunnar
Carlsson, Ralph Cohen, and Ib Madsen.Comment: After revisions, now 21 pages, 5 figure
Isoperimetric Inequalities in Simplicial Complexes
In graph theory there are intimate connections between the expansion
properties of a graph and the spectrum of its Laplacian. In this paper we
define a notion of combinatorial expansion for simplicial complexes of general
dimension, and prove that similar connections exist between the combinatorial
expansion of a complex, and the spectrum of the high dimensional Laplacian
defined by Eckmann. In particular, we present a Cheeger-type inequality, and a
high-dimensional Expander Mixing Lemma. As a corollary, using the work of Pach,
we obtain a connection between spectral properties of complexes and Gromov's
notion of geometric overlap. Using the work of Gunder and Wagner, we give an
estimate for the combinatorial expansion and geometric overlap of random
Linial-Meshulam complexes