3,969 research outputs found

### Generating Diophantine Sets by Virus Machines

Virus Machines are a computational paradigm inspired by
the manner in which viruses replicate and transmit from one host cell to
another. This paradigm provides non-deterministic sequential devices.
Non-restricted virus machines are unbounded virus machines, in the
sense that no restriction on the number of hosts, the number of instructions
and the number of viruses contained in any host along any computation
is placed on them. The computational completeness of these
machines has been obtained by simulating register machines. In this
paper, virus machines as set generating devices are considered. Then,
the universality of non-restricted virus machines is proved by showing
that they can compute all diophantine sets, which the MRDP theorem
proves that coincide with the recursively enumerable sets.Ministerio de Economía y Competitividad TIN2012- 3743

### Scheduling Packets with Values and Deadlines in Size-bounded Buffers

Motivated by providing quality-of-service differentiated services in the
Internet, we consider buffer management algorithms for network switches. We
study a multi-buffer model. A network switch consists of multiple size-bounded
buffers such that at any time, the number of packets residing in each
individual buffer cannot exceed its capacity. Packets arrive at the network
switch over time; they have values, deadlines, and designated buffers. In each
time step, at most one pending packet is allowed to be sent and this packet can
be from any buffer. The objective is to maximize the total value of the packets
sent by their respective deadlines. A 9.82-competitive online algorithm has
been provided for this model (Azar and Levy. SWAT 2006), but no offline
algorithms have been known yet. In this paper, We study the offline setting of
the multi-buffer model. Our contributions include a few optimal offline
algorithms for some variants of the model. Each variant has its unique and
interesting algorithmic feature. These offline algorithms help us understand
the model better in designing online algorithms.Comment: 7 page

### Monte Carlo Algorithm for Simulating Reversible Aggregation of Multisite Particles

We present an efficient and exact Monte Carlo algorithm to simulate
reversible aggregation of particles with dedicated binding sites. This method
introduces a novel data structure of dynamic bond tree to record clusters and
sequences of bond formations. The algorithm achieves a constant time cost for
processing cluster association and a cost between $\mathcal{O}(\log M)$ and
$\mathcal{O}(M)$ for processing bond dissociation in clusters with $M$ bonds.
The algorithm is statistically exact and can reproduce results obtained by the
standard method. We applied the method to simulate a trivalent ligand and a
bivalent receptor clustering system and obtained an average scaling of
$\mathcal{O}(M^{0.45})$ for processing bond dissociation in acyclic
aggregation, compared to a linear scaling with the cluster size in standard
methods. The algorithm also demands substantially less memory than the
conventional method.Comment: 8 pages, 3 figure

### Parallel Metric Tree Embedding based on an Algebraic View on Moore-Bellman-Ford

A \emph{metric tree embedding} of expected \emph{stretch~$\alpha \geq 1$}
maps a weighted $n$-node graph $G = (V, E, \omega)$ to a weighted tree $T =
(V_T, E_T, \omega_T)$ with $V \subseteq V_T$ such that, for all $v,w \in V$,
$\operatorname{dist}(v, w, G) \leq \operatorname{dist}(v, w, T)$ and
$operatorname{E}[\operatorname{dist}(v, w, T)] \leq \alpha
\operatorname{dist}(v, w, G)$. Such embeddings are highly useful for designing
fast approximation algorithms, as many hard problems are easy to solve on tree
instances. However, to date the best parallel $(\operatorname{polylog}
n)$-depth algorithm that achieves an asymptotically optimal expected stretch of
$\alpha \in \operatorname{O}(\log n)$ requires $\operatorname{\Omega}(n^2)$
work and a metric as input.
In this paper, we show how to achieve the same guarantees using
$\operatorname{polylog} n$ depth and $\operatorname{\tilde{O}}(m^{1+\epsilon})$
work, where $m = |E|$ and $\epsilon > 0$ is an arbitrarily small constant.
Moreover, one may further reduce the work to $\operatorname{\tilde{O}}(m +
n^{1+\epsilon})$ at the expense of increasing the expected stretch to
$\operatorname{O}(\epsilon^{-1} \log n)$.
Our main tool in deriving these parallel algorithms is an algebraic
characterization of a generalization of the classic Moore-Bellman-Ford
algorithm. We consider this framework, which subsumes a variety of previous
"Moore-Bellman-Ford-like" algorithms, to be of independent interest and discuss
it in depth. In our tree embedding algorithm, we leverage it for providing
efficient query access to an approximate metric that allows sampling the tree
using $\operatorname{polylog} n$ depth and $\operatorname{\tilde{O}}(m)$ work.
We illustrate the generality and versatility of our techniques by various
examples and a number of additional results

### Vector Layout in Virtual-Memory Systems for Data-Parallel Computing

In a data-parallel computer with virtual memory, the way in which vectors are laid out on the disk system affects the performance of data-parallel operations. We present a general method of vector layout called banded layout, in which we divide a vector into bands of a number of consecutive vector elements laid out in column-major order, and we analyze the effect of the band size on the major classes of data-parallel operations. We find that although the best band size varies among the operations, choosing fairly small band sizes—at most a track—works well in general

### Determining an Out-of-Core FFT Decomposition Strategy for Parallel Disks by Dynamic Programming

We present an out-of-core FFT algorithm based on the in-core FFT method developed by Swarztrauber. Our algorithm uses a recursive divide-and-conquer strategy, and each stage in the recursion presents several possibilities for how to split the problem into subproblems. We give a recurrence for the algorithm\u27s I/O complexity on the Parallel Disk Model and show how to use dynamic programming to determine optimal splits at each recursive stage. The algorithm to determine the optimal splits takes only Theta(lg^2 N) time for an N-point FFT, and it is practical. The out-of-core FFT algorithm itself takes considerably longer

### Planning of vehicle routing with backup provisioning using wireless sensor technologies

Wireless sensor technologies can be used by intelligent transportation systems to provide innovative services that lead to improvements in road safety and congestion, increasing end-user satisfaction. In this article, we address vehicle routing with backup provisioning, where the possibility of reacting to overloading/overcrowding of vehicles at certain stops is considered. This is based on the availability of vehicle load information, which can be captured using wireless sensor technologies. After discussing the infrastructure and monitoring tool, the problem is mathematically formalized, and a heuristic algorithm using local search procedures is proposed. Results show that planning routes with backup provisioning can allow fast response to overcrowding while reducing costs. Therefore, sustainable urban mobility, with efficient use of resources, can be provided while increasing the quality of service perceived by users.FCT (Foundation for Science and Technology) from Portugal within CEOT (Center for Electronic, Optoelectronic and Telecommunications); [UID/MULTI/00631/2013

### Near-equilibrium measurements of nonequilibrium free energy

A central endeavor of thermodynamics is the measurement of free energy
changes. Regrettably, although we can measure the free energy of a system in
thermodynamic equilibrium, typically all we can say about the free energy of a
non-equilibrium ensemble is that it is larger than that of the same system at
equilibrium. Herein, we derive a formally exact expression for the probability
distribution of a driven system, which involves path ensemble averages of the
work over trajectories of the time-reversed system. From this we find a simple
near-equilibrium approximation for the free energy in terms of an excess mean
time-reversed work, which can be experimentally measured on real systems. With
analysis and computer simulation, we demonstrate the accuracy of our
approximations for several simple models.Comment: 5 pages, 3 figure

### A Scalable Asynchronous Distributed Algorithm for Topic Modeling

Learning meaningful topic models with massive document collections which
contain millions of documents and billions of tokens is challenging because of
two reasons: First, one needs to deal with a large number of topics (typically
in the order of thousands). Second, one needs a scalable and efficient way of
distributing the computation across multiple machines. In this paper we present
a novel algorithm F+Nomad LDA which simultaneously tackles both these problems.
In order to handle large number of topics we use an appropriately modified
Fenwick tree. This data structure allows us to sample from a multinomial
distribution over $T$ items in $O(\log T)$ time. Moreover, when topic counts
change the data structure can be updated in $O(\log T)$ time. In order to
distribute the computation across multiple processor we present a novel
asynchronous framework inspired by the Nomad algorithm of
\cite{YunYuHsietal13}. We show that F+Nomad LDA significantly outperform
state-of-the-art on massive problems which involve millions of documents,
billions of words, and thousands of topics

### Solving mazes with memristors: a massively-parallel approach

Solving mazes is not just a fun pastime. Mazes are prototype models in graph theory, topology, robotics, traffic optimization, psychology, and in many other areas of science and technology. However, when maze complexity increases their solution becomes cumbersome and very time consuming. Here, we show that a network of memristors - resistors with memory - can solve such a non-trivial problem quite easily. In particular, maze solving by the network of memristors occurs in a massively parallel fashion since all memristors in the network participate simultaneously in the calculation. The result of the calculation is then recorded into the memristors’ states, and can be used and/or recovered at a later time. Furthermore, the network of memristors finds all possible solutions in multiple-solution mazes, and sorts out the solution paths according to their length. Our results demonstrate not only the first application of memristive networks to the field of massively-parallel computing, but also a novel algorithm to solve mazes which could find applications in different research fields

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