4,560 research outputs found
The Forcing Weak Edge Detour Number of a Graph
The forcing weak edge detour numbers of certain classes of graphs are determined
Connected Weak Edge Detour Number of a Graph
Certain general properties of the detour distance, weak edge detour set, connected weak edge detour set, connected weak edge detour number and connected weak edge detour basis of graphs are studied in this paper. Their relationship with the detour diameter is discussed. It is proved that for each pair of integers k and n with 2 <= k <= n, there exists a connected graph G of order n with cdnw(G)=k. It is also proved that for any three positive integers R,D,k such that k >= D and R < D <= 2R, there exists a connected graph G with radD (G) = R, diamD G = D and cdnw(G)=k
Bridging the Gap between Programming Languages and Hardware Weak Memory Models
We develop a new intermediate weak memory model, IMM, as a way of
modularizing the proofs of correctness of compilation from concurrent
programming languages with weak memory consistency semantics to mainstream
multi-core architectures, such as POWER and ARM. We use IMM to prove the
correctness of compilation from the promising semantics of Kang et al. to POWER
(thereby correcting and improving their result) and ARMv7, as well as to the
recently revised ARMv8 model. Our results are mechanized in Coq, and to the
best of our knowledge, these are the first machine-verified compilation
correctness results for models that are weaker than x86-TSO
Shortest Reconfiguration of Sliding Tokens on a Caterpillar
Suppose that we are given two independent sets I_b and I_r of a graph such
that |I_b|=|I_r|, and imagine that a token is placed on each vertex in |I_b|.
Then, the sliding token problem is to determine whether there exists a sequence
of independent sets which transforms I_b into I_r so that each independent set
in the sequence results from the previous one by sliding exactly one token
along an edge in the graph. The sliding token problem is one of the
reconfiguration problems that attract the attention from the viewpoint of
theoretical computer science. The reconfiguration problems tend to be
PSPACE-complete in general, and some polynomial time algorithms are shown in
restricted cases. Recently, the problems that aim at finding a shortest
reconfiguration sequence are investigated. For the 3SAT problem, a trichotomy
for the complexity of finding the shortest sequence has been shown, that is, it
is in P, NP-complete, or PSPACE-complete in certain conditions. In general,
even if it is polynomial time solvable to decide whether two instances are
reconfigured with each other, it can be NP-complete to find a shortest sequence
between them. Namely, finding a shortest sequence between two independent sets
can be more difficult than the decision problem of reconfigurability between
them. In this paper, we show that the problem for finding a shortest sequence
between two independent sets is polynomial time solvable for some graph classes
which are subclasses of the class of interval graphs. More precisely, we can
find a shortest sequence between two independent sets on a graph G in
polynomial time if either G is a proper interval graph, a trivially perfect
graph, or a caterpillar. As far as the authors know, this is the first
polynomial time algorithm for the shortest sliding token problem for a graph
class that requires detours
Arrangements Of Minors In The Positive Grassmannian And a Triangulation of The Hypersimplex
The structure of zero and nonzero minors in the Grassmannian leads to rich
combinatorics of matroids. In this paper, we investigate an even richer
structure of possible equalities and inequalities between the minors in the
positive Grassmannian. It was previously shown that arrangements of equal
minors of largest value are in bijection with the simplices in a certain
triangulation of the hypersimplex that was studied by Stanley, Sturmfels, Lam
and Postnikov. Here we investigate the entire set of arrangements and its
relations with this triangulation. First, we show that second largest minors
correspond to the facets of the simplices. We then introduce the notion of
cubical distance on the dual graph of the triangulation, and study its
relations with the arrangement of t-th largest minors. Finally, we show that
arrangements of largest minors induce a structure of partially ordered sets on
the entire collection of minors. We use the Lam and Postnikov circuit
triangulation of the hypersimplex to describe a 2-dimensional grid structure of
this poset
SPIDER: Fault Resilient SDN Pipeline with Recovery Delay Guarantees
When dealing with node or link failures in Software Defined Networking (SDN),
the network capability to establish an alternative path depends on controller
reachability and on the round trip times (RTTs) between controller and involved
switches. Moreover, current SDN data plane abstractions for failure detection
(e.g. OpenFlow "Fast-failover") do not allow programmers to tweak switches'
detection mechanism, thus leaving SDN operators still relying on proprietary
management interfaces (when available) to achieve guaranteed detection and
recovery delays. We propose SPIDER, an OpenFlow-like pipeline design that
provides i) a detection mechanism based on switches' periodic link probing and
ii) fast reroute of traffic flows even in case of distant failures, regardless
of controller availability. SPIDER can be implemented using stateful data plane
abstractions such as OpenState or Open vSwitch, and it offers guaranteed short
(i.e. ms) failure detection and recovery delays, with a configurable trade off
between overhead and failover responsiveness. We present here the SPIDER
pipeline design, behavioral model, and analysis on flow tables' memory impact.
We also implemented and experimentally validated SPIDER using OpenState (an
OpenFlow 1.3 extension for stateful packet processing), showing numerical
results on its performance in terms of recovery latency and packet losses.Comment: 8 page
Extended Dijkstra algorithm and Moore-Bellman-Ford algorithm
Study the general single-source shortest path problem. Firstly, define a path
function on a set of some path with same source on a graph, and develop a kind
of general single-source shortest path problem (GSSSP) on the defined path
function. Secondly, following respectively the approaches of the well known
Dijkstra's algorithm and Moore-Bellman-Ford algorithm, design an extended
Dijkstra's algorithm (EDA) and an extended Moore-Bellman-Ford algorithm (EMBFA)
to solve the problem GSSSP under certain given conditions. Thirdly, introduce a
few concepts, such as order-preserving in last road (OPLR) of path function,
and so on. And under the assumption that the value of related path function for
any path can be obtained in time, prove respectively the algorithm EDA
solving the problem GSSSP in time and the algorithm EMBFA solving
the problem GSSSP in time. Finally, some applications of the
designed algorithms are shown with a few examples. What we done can improve
both the researchers and the applications of the shortest path theory.Comment: 25 page
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