6,185 research outputs found
Distance-Preserving Graph Contractions
Compression and sparsification algorithms are frequently applied in a preprocessing step before analyzing or optimizing large networks/graphs.
In this paper we propose and study a new framework contracting edges of a graph (merging vertices into super-vertices) with the goal of preserving pairwise distances as accurately as possible.
Formally, given an edge-weighted graph, the contraction should guarantee that for any two vertices at distance d, the corresponding super-vertices remain at distance at least varphi(d) in the contracted graph, where varphi is a tolerance function bounding the permitted distance distortion.
We present a comprehensive picture of the algorithmic complexity of the contraction problem for affine tolerance functions varphi(x)=x/alpha-beta, where alpha geq 1 and beta geq 0 are arbitrary real-valued parameters.
Specifically, we present polynomial-time algorithms for trees as well as hardness and inapproximability results for different graph classes, precisely separating easy and hard cases.
Further we analyze the asymptotic behavior of the size of contractions, and find efficient algorithms to compute (non-optimal) contractions despite our hardness results
Fixed Points of Integral Type Contractions in Uniform Spaces with a Graph
In this paper, we discuss the existence of fixed points for integral type
contractions in uniform spaces endowed with both a graph and an -distance.
We also give two sufficient conditions under which the fixed point is unique.
Our main results generalize some recent metric fixed point theorems.Comment: 10 page
Myopic Models of Population Dynamics on Infinite Networks
Reaction-diffusion equations are treated on infinite networks using semigroup
methods. To blend high fidelity local analysis with coarse remote modeling,
initial data and solutions come from a uniformly closed algebra generated by
functions which are flat at infinity. The algebra is associated with a
compactification of the network which facilitates the description of spatial
asymptotics. Diffusive effects disappear at infinity, greatly simplifying the
remote dynamics. Accelerated diffusion models with conventional eigenfunctions
expansions are constructed to provide opportunities for finite dimensional
approximation.Comment: 36 pages. arXiv admin note: text overlap with arXiv:1109.313
- …