26,826 research outputs found
Performance Considerations for Gigabyte per Second Transcontinental Disk-to-Disk File Transfers
Moving data from CERN to Pasadena at a gigabyte per second using the next
generation Internet requires good networking and good disk IO. Ten Gbps
Ethernet and OC192 links are in place, so now it is simply a matter of
programming. This report describes our preliminary work and measurements in
configuring the disk subsystem for this effort. Using 24 SATA disks at each
endpoint we are able to locally read and write an NTFS volume is striped across
24 disks at 1.2 GBps. A 32-disk stripe delivers 1.7 GBps. Experiments on higher
performance and higher-capacity systems deliver up to 3.5 GBps
Randomness and Complexity in Networks
I start by reviewing some basic properties of random graphs. I then consider
the role of random walks in complex networks and show how they may be used to
explain why so many long tailed distributions are found in real data sets. The
key idea is that in many cases the process involves copying of properties of
near neighbours in the network and this is a type of short random walk which in
turn produce a natural preferential attachment mechanism. Applying this to
networks of fixed size I show that copying and innovation are processes with
special mathematical properties which include the ability to solve a simple
model exactly for any parameter values and at any time. I finish by looking at
variations of this basic model.Comment: Survey paper based on talk given at the workshop on ``Stochastic
Networks and Internet Technology'', Centro di Ricerca Matematica Ennio De
Giorgi, Matematica nelle Scienze Naturali e Sociali, Pisa, 17th - 21st
September 2007. To appear in proceeding
An Algorithm for Odd Graceful Labeling of the Union of Paths and Cycles
In 1991, Gnanajothi [4] proved that the path graph P_n with n vertex and n-1
edge is odd graceful, and the cycle graph C_m with m vertex and m edges is odd
graceful if and only if m even, she proved the cycle graph is not graceful if m
odd. In this paper, firstly, we studied the graph C_m P_m when m = 4,
6,8,10 and then we proved that the graph C_ P_n is odd graceful if m is
even. Finally, we described an algorithm to label the vertices and the edges of
the vertex set V(C_m P_n) and the edge set E(C_m P_n).Comment: 9 Pages, JGraph-Hoc Journa
I/O-optimal algorithms on grid graphs
Given a graph of which the n vertices form a regular two-dimensional grid,
and in which each (possibly weighted and/or directed) edge connects a vertex to
one of its eight neighbours, the following can be done in O(scan(n)) I/Os,
provided M = Omega(B^2): computation of shortest paths with non-negative edge
weights from a single source, breadth-first traversal, computation of a minimum
spanning tree, topological sorting, time-forward processing (if the input is a
plane graph), and an Euler tour (if the input graph is a tree). The
minimum-spanning tree algorithm is cache-oblivious. The best previously
published algorithms for these problems need Theta(sort(n)) I/Os. Estimates of
the actual I/O volume show that the new algorithms may often be very efficient
in practice.Comment: 12 pages' extended abstract plus 12 pages' appendix with details,
proofs and calculations. Has not been published in and is currently not under
review of any conference or journa
Enumerating Maximal Bicliques from a Large Graph using MapReduce
We consider the enumeration of maximal bipartite cliques (bicliques) from a
large graph, a task central to many practical data mining problems in social
network analysis and bioinformatics. We present novel parallel algorithms for
the MapReduce platform, and an experimental evaluation using Hadoop MapReduce.
Our algorithm is based on clustering the input graph into smaller sized
subgraphs, followed by processing different subgraphs in parallel. Our
algorithm uses two ideas that enable it to scale to large graphs: (1) the
redundancy in work between different subgraph explorations is minimized through
a careful pruning of the search space, and (2) the load on different reducers
is balanced through the use of an appropriate total order among the vertices.
Our evaluation shows that the algorithm scales to large graphs with millions of
edges and tens of mil- lions of maximal bicliques. To our knowledge, this is
the first work on maximal biclique enumeration for graphs of this scale.Comment: A preliminary version of the paper was accepted at the Proceedings of
the 3rd IEEE International Congress on Big Data 201
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