643 research outputs found
Compositional competitiveness for distributed algorithms
We define a measure of competitive performance for distributed algorithms
based on throughput, the number of tasks that an algorithm can carry out in a
fixed amount of work. This new measure complements the latency measure of Ajtai
et al., which measures how quickly an algorithm can finish tasks that start at
specified times. The novel feature of the throughput measure, which
distinguishes it from the latency measure, is that it is compositional: it
supports a notion of algorithms that are competitive relative to a class of
subroutines, with the property that an algorithm that is k-competitive relative
to a class of subroutines, combined with an l-competitive member of that class,
gives a combined algorithm that is kl-competitive.
In particular, we prove the throughput-competitiveness of a class of
algorithms for collect operations, in which each of a group of n processes
obtains all values stored in an array of n registers. Collects are a
fundamental building block of a wide variety of shared-memory distributed
algorithms, and we show that several such algorithms are competitive relative
to collects. Inserting a competitive collect in these algorithms gives the
first examples of competitive distributed algorithms obtained by composition
using a general construction.Comment: 33 pages, 2 figures; full version of STOC 96 paper titled "Modular
competitiveness for distributed algorithms.
On-Line File Caching
In the on-line file-caching problem problem, the input is a sequence of
requests for files, given on-line (one at a time). Each file has a non-negative
size and a non-negative retrieval cost. The problem is to decide which files to
keep in a fixed-size cache so as to minimize the sum of the retrieval costs for
files that are not in the cache when requested. The problem arises in web
caching by browsers and by proxies. This paper describes a natural
generalization of LRU called Landlord and gives an analysis showing that it has
an optimal performance guarantee (among deterministic on-line algorithms).
The paper also gives an analysis of the algorithm in a so-called ``loosely''
competitive model, showing that on a ``typical'' cache size, either the
performance guarantee is O(1) or the total retrieval cost is insignificant.Comment: ACM-SIAM Symposium on Discrete Algorithms (1998
Quantum Algorithms for Identifying Hidden Strings with Applications to Matroid Problems
In this paper, we explore quantum speedups for the problem, inspired by
matroid theory, of identifying a pair of -bit binary strings that are
promised to have the same number of 1s and differ in exactly two bits, by using
the max inner product oracle and the sub-set oracle. More specifically, given
two string satisfying the above constraints, for any
the max inner product oracle returns the max
value between and , and the sub-set oracle
indicates whether the index set of the 1s in is a subset of that in or
. We present a quantum algorithm consuming queries to the max inner
product oracle for identifying the pair , and prove that any
classical algorithm requires queries. Also, we present a
quantum algorithm consuming queries to the subset
oracle, and prove that any classical algorithm requires at least
queries. Therefore, quantum speedups are revealed in the two oracle models.
Furthermore, the above results are applied to the problem in matroid theory of
finding all the bases of a 2-bases matroid, where a matroid is called -bases
if it has bases
School of Law Annual Report 1995-1996
The annual report for the University of New Mexico School of Law for the period July 1995 through June 1996
Post-quantum cryptography
Cryptography is essential for the security of online communication, cars and implanted medical devices. However, many commonly used cryptosystems will be completely broken once large quantum computers exist. Post-quantum cryptography is cryptography under the assumption that the attacker has a large quantum computer; post-quantum cryptosystems strive to remain secure even in this scenario. This relatively young research area has seen some successes in identifying mathematical operations for which quantum algorithms offer little advantage in speed, and then building cryptographic systems around those. The central challenge in post-quantum cryptography is to meet demands for cryptographic usability and flexibility without sacrificing confidence.</p
On the role of entanglement and correlations in mixed-state quantum computation
In a quantum computation with pure states, the generation of large amounts of
entanglement is known to be necessary for a speedup with respect to classical
computations. However, examples of quantum computations with mixed states are
known, such as the deterministic computation with one quantum qubit (DQC1)
model [Knill and Laflamme, Phys. Rev. Lett. 81, 5672 (1998)], in which
entanglement is at most marginally present, and yet a computational speedup is
believed to occur. Correlations, and not entanglement, have been identified as
a necessary ingredient for mixed-state quantum computation speedups. Here we
show that correlations, as measured through the operator Schmidt rank, are
indeed present in large amounts in the DQC1 circuit. This provides evidence for
the preclusion of efficient classical simulation of DQC1 by means of a whole
class of classical simulation algorithms, thereby reinforcing the conjecture
that DQC1 leads to a genuine quantum computational speedup
A Taxonomy of Workflow Management Systems for Grid Computing
With the advent of Grid and application technologies, scientists and
engineers are building more and more complex applications to manage and process
large data sets, and execute scientific experiments on distributed resources.
Such application scenarios require means for composing and executing complex
workflows. Therefore, many efforts have been made towards the development of
workflow management systems for Grid computing. In this paper, we propose a
taxonomy that characterizes and classifies various approaches for building and
executing workflows on Grids. We also survey several representative Grid
workflow systems developed by various projects world-wide to demonstrate the
comprehensiveness of the taxonomy. The taxonomy not only highlights the design
and engineering similarities and differences of state-of-the-art in Grid
workflow systems, but also identifies the areas that need further research.Comment: 29 pages, 15 figure
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