69 research outputs found
Optimal Acyclic Hamiltonian Path Completion for Outerplanar Triangulated st-Digraphs (with Application to Upward Topological Book Embeddings)
Given an embedded planar acyclic digraph G, we define the problem of "acyclic
hamiltonian path completion with crossing minimization (Acyclic-HPCCM)" to be
the problem of determining an hamiltonian path completion set of edges such
that, when these edges are embedded on G, they create the smallest possible
number of edge crossings and turn G to a hamiltonian digraph. Our results
include:
--We provide a characterization under which a triangulated st-digraph G is
hamiltonian.
--For an outerplanar triangulated st-digraph G, we define the st-polygon
decomposition of G and, based on its properties, we develop a linear-time
algorithm that solves the Acyclic-HPCCM problem with at most one crossing per
edge of G.
--For the class of st-planar digraphs, we establish an equivalence between
the Acyclic-HPCCM problem and the problem of determining an upward 2-page
topological book embedding with minimum number of spine crossings. We infer
(based on this equivalence) for the class of outerplanar triangulated
st-digraphs an upward topological 2-page book embedding with minimum number of
spine crossings and at most one spine crossing per edge.
To the best of our knowledge, it is the first time that edge-crossing
minimization is studied in conjunction with the acyclic hamiltonian completion
problem and the first time that an optimal algorithm with respect to spine
crossing minimization is presented for upward topological book embeddings
Occupational Fraud Detection Through Visualization
Occupational fraud affects many companies worldwide causing them economic
loss and liability issues towards their customers and other involved entities.
Detecting internal fraud in a company requires significant effort and,
unfortunately cannot be entirely prevented. The internal auditors have to
process a huge amount of data produced by diverse systems, which are in most
cases in textual form, with little automated support. In this paper, we exploit
the advantages of information visualization and present a system that aims to
detect occupational fraud in systems which involve a pair of entities (e.g., an
employee and a client) and periodic activity. The main visualization is based
on a spiral system on which the events are drawn appropriately according to
their time-stamp. Suspicious events are considered those which appear along the
same radius or on close radii of the spiral. Before producing the
visualization, the system ranks both involved entities according to the
specifications of the internal auditor and generates a video file of the
activity such that events with strong evidence of fraud appear first in the
video. The system is also equipped with several different visualizations and
mechanisms in order to meet the requirements of an internal fraud detection
system
Optimal Algorithms for Multipacket Routing Problems on Rings
We study multipacket routing problems. We divide the multipacket routing problem into two classes, namely, distance limited and bisection limited routing problems. Then, we concentrate on rings of processors. We prove a new lower bound of 2n/ 3 routing steps for the case of distance limited routing problems. We also give an algorithm that tightens this lower bound. For bisection limited problems the lower bound is kn/ 4,k \u3e2, where k is the number of packets per processor. The trivial algorithm needs in the worst case k | n /2| steps to terminate. An algorithm that completes the routing in kn /4 + 2.5 n routing steps is given. We define the class of pure routing algorithms and we demonstrate that new lower bounds hold if the routing is to be done by an algorithm in this class
Many-to-One Boundary Labeling with Backbones
In this paper we study \emph{many-to-one boundary labeling with backbone
leaders}. In this new many-to-one model, a horizontal backbone reaches out of
each label into the feature-enclosing rectangle. Feature points that need to be
connected to this label are linked via vertical line segments to the backbone.
We present dynamic programming algorithms for label number and total leader
length minimization of crossing-free backbone labelings. When crossings are
allowed, we aim to obtain solutions with the minimum number of crossings. This
can be achieved efficiently in the case of fixed label order, however, in the
case of flexible label order we show that minimizing the number of leader
crossings is NP-hard.Comment: 23 pages, 10 figures, this is the full version of a paper that is
about to appear in GD'1
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