24,301 research outputs found
Implicit Decomposition for Write-Efficient Connectivity Algorithms
The future of main memory appears to lie in the direction of new technologies
that provide strong capacity-to-performance ratios, but have write operations
that are much more expensive than reads in terms of latency, bandwidth, and
energy. Motivated by this trend, we propose sequential and parallel algorithms
to solve graph connectivity problems using significantly fewer writes than
conventional algorithms. Our primary algorithmic tool is the construction of an
-sized "implicit decomposition" of a bounded-degree graph on
nodes, which combined with read-only access to enables fast answers to
connectivity and biconnectivity queries on . The construction breaks the
linear-write "barrier", resulting in costs that are asymptotically lower than
conventional algorithms while adding only a modest cost to querying time. For
general non-sparse graphs on edges, we also provide the first writes
and operations parallel algorithms for connectivity and biconnectivity.
These algorithms provide insight into how applications can efficiently process
computations on large graphs in systems with read-write asymmetry
Structure of Business Firm Networks and Scale-Free Models
We study the structure of business firm networks and scale-free models with
degree distribution using the method of
-shell decomposition.We find that the Life Sciences industry network consist
of three components: a ``nucleus,'' which is a small well connected subgraph,
``tendrils,'' which are small subgraphs consisting of small degree nodes
connected exclusively to the nucleus, and a ``bulk body'' which consists of the
majority of nodes. At the same time we do not observe the above structure in
the Information and Communication Technology sector of industry. We also
conduct a systematic study of these three components in random scale-free
networks. Our results suggest that the sizes of the nucleus and the tendrils
decrease as increases and disappear for . We compare
the -shell structure of random scale-free model networks with two real world
business firm networks in the Life Sciences and in the Information and
Communication Technology sectors. Our results suggest that the observed
behavior of the -shell structure in the two industries is consistent with a
recently proposed growth model that assumes the coexistence of both
preferential and random agreements in the evolution of industrial networks
Parallel implementation of the TRANSIMS micro-simulation
This paper describes the parallel implementation of the TRANSIMS traffic
micro-simulation. The parallelization method is domain decomposition, which
means that each CPU of the parallel computer is responsible for a different
geographical area of the simulated region. We describe how information between
domains is exchanged, and how the transportation network graph is partitioned.
An adaptive scheme is used to optimize load balancing. We then demonstrate how
computing speeds of our parallel micro-simulations can be systematically
predicted once the scenario and the computer architecture are known. This makes
it possible, for example, to decide if a certain study is feasible with a
certain computing budget, and how to invest that budget. The main ingredients
of the prediction are knowledge about the parallel implementation of the
micro-simulation, knowledge about the characteristics of the partitioning of
the transportation network graph, and knowledge about the interaction of these
quantities with the computer system. In particular, we investigate the
differences between switched and non-switched topologies, and the effects of 10
Mbit, 100 Mbit, and Gbit Ethernet. keywords: Traffic simulation, parallel
computing, transportation planning, TRANSIM
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