67 research outputs found
Reconstruction of permutations distorted by single transposition errors
The reconstruction problem for permutations on elements from their
erroneous patterns which are distorted by transpositions is presented in this
paper. It is shown that for any an unknown permutation is uniquely
reconstructible from 4 distinct permutations at transposition distance at most
one from the unknown permutation. The {\it transposition distance} between two
permutations is defined as the least number of transpositions needed to
transform one into the other. The proposed approach is based on the
investigation of structural properties of a corresponding Cayley graph. In the
case of at most two transposition errors it is shown that
erroneous patterns are required in order to reconstruct an unknown permutation.
Similar results are obtained for two particular cases when permutations are
distorted by given transpositions. These results confirm some bounds for
regular graphs which are also presented in this paper.Comment: 5 pages, Report of paper presented at ISIT-200
06201 Abstracts Collection -- Combinatorial and Algorithmic Foundations of Pattern and Association Discovery
From 15.05.06 to 20.05.06, the Dagstuhl Seminar 06201 ``Combinatorial and Algorithmic Foundations of Pattern and Association Discovery\u27\u27 was held
in the International Conference and Research Center (IBFI), Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Codes with Locality for Two Erasures
In this paper, we study codes with locality that can recover from two
erasures via a sequence of two local, parity-check computations. By a local
parity-check computation, we mean recovery via a single parity-check equation
associated to small Hamming weight. Earlier approaches considered recovery in
parallel; the sequential approach allows us to potentially construct codes with
improved minimum distance. These codes, which we refer to as locally
2-reconstructible codes, are a natural generalization along one direction, of
codes with all-symbol locality introduced by Gopalan \textit{et al}, in which
recovery from a single erasure is considered. By studying the Generalized
Hamming Weights of the dual code, we derive upper bounds on the minimum
distance of locally 2-reconstructible codes and provide constructions for a
family of codes based on Tur\'an graphs, that are optimal with respect to this
bound. The minimum distance bound derived here is universal in the sense that
no code which permits all-symbol local recovery from erasures can have
larger minimum distance regardless of approach adopted. Our approach also leads
to a new bound on the minimum distance of codes with all-symbol locality for
the single-erasure case.Comment: 14 pages, 3 figures, Updated for improved readabilit
Reconstructibility of matroid polytopes
We specify what is meant for a polytope to be reconstructible from its graph or dual graph, and we introduce the problem of class reconstructibility; i.e., the face lattice of the polytope can be determined from the (dual) graph within a given class. We provide examples of cubical polytopes that are not reconstructible from their dual graphs. Furthermore, we show that matroid (base) polytopes are not reconstructible from their graphs and not class reconstructible from their dual graphs; our counterexamples include hypersimplices. Additionally, we prove that matroid polytopes are class reconstructible from their graphs, and we present an O(n3) algorithm that computes the vertices of a matroid polytope from its n-vertex graph. Moreover, our proof includes a characterization of all matroids with isomorphic basis exchange graphs. © 2022 Society for Industrial and Applied Mathematic
Hypomorphisms, orbits, and reconstruction
AbstractGraphs G and H are hypomorphic if there is a bijection φ: V(G) → V(H) such that G − u ≅ H − φ(u), for all u ∈ V(G). The reconstruction conjecture states that hypomorphic graphs are isomorphic, if G has at least three vertices. We investigate properties of the isomorphisms G − u ≅ H − φ(u), and their relation to the reconstructibility of G
Reconstructibility of matroid polytopes
We specify what is meant for a polytope to be reconstructible from its graph
or dual graph. And we introduce the problem of class reconstructibility, i.e.,
the face lattice of the polytope can be determined from the (dual) graph within
a given class. We provide examples of cubical polytopes that are not
reconstructible from their dual graphs. Furthermore, we show that matroid
(base) polytopes are not reconstructible from their graphs and not class
reconstructible from their dual graphs; our counterexamples include
hypersimplices. Additionally, we prove that matroid polytopes are class
reconstructible from their graphs, and we present a algorithm that
computes the vertices of a matroid polytope from its -vertex graph.
Moreover, our proof includes a characterisation of all matroids with isomorphic
basis exchange graphs.Comment: 22 pages, 5 figure
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