31,586 research outputs found
Soft Contract Verification
Behavioral software contracts are a widely used mechanism for governing the
flow of values between components. However, run-time monitoring and enforcement
of contracts imposes significant overhead and delays discovery of faulty
components to run-time.
To overcome these issues, we present soft contract verification, which aims
to statically prove either complete or partial contract correctness of
components, written in an untyped, higher-order language with first-class
contracts. Our approach uses higher-order symbolic execution, leveraging
contracts as a source of symbolic values including unknown behavioral values,
and employs an updatable heap of contract invariants to reason about
flow-sensitive facts. We prove the symbolic execution soundly approximates the
dynamic semantics and that verified programs can't be blamed.
The approach is able to analyze first-class contracts, recursive data
structures, unknown functions, and control-flow-sensitive refinements of
values, which are all idiomatic in dynamic languages. It makes effective use of
an off-the-shelf solver to decide problems without heavy encodings. The
approach is competitive with a wide range of existing tools---including type
systems, flow analyzers, and model checkers---on their own benchmarks.Comment: ICFP '14, September 1-6, 2014, Gothenburg, Swede
Towards a Holistic Integration of Spreadsheets with Databases: A Scalable Storage Engine for Presentational Data Management
Spreadsheet software is the tool of choice for interactive ad-hoc data
management, with adoption by billions of users. However, spreadsheets are not
scalable, unlike database systems. On the other hand, database systems, while
highly scalable, do not support interactivity as a first-class primitive. We
are developing DataSpread, to holistically integrate spreadsheets as a
front-end interface with databases as a back-end datastore, providing
scalability to spreadsheets, and interactivity to databases, an integration we
term presentational data management (PDM). In this paper, we make a first step
towards this vision: developing a storage engine for PDM, studying how to
flexibly represent spreadsheet data within a database and how to support and
maintain access by position. We first conduct an extensive survey of
spreadsheet use to motivate our functional requirements for a storage engine
for PDM. We develop a natural set of mechanisms for flexibly representing
spreadsheet data and demonstrate that identifying the optimal representation is
NP-Hard; however, we develop an efficient approach to identify the optimal
representation from an important and intuitive subclass of representations. We
extend our mechanisms with positional access mechanisms that don't suffer from
cascading update issues, leading to constant time access and modification
performance. We evaluate these representations on a workload of typical
spreadsheets and spreadsheet operations, providing up to 20% reduction in
storage, and up to 50% reduction in formula evaluation time
NLO electroweak corrections in extended Higgs Sectors with RECOLA2
We present the computer code RECOLA2 along with the first NLO electroweak
corrections to Higgs production in vector-boson fusion and updated results for
Higgs strahlung in the Two-Higgs-Doublet Model and Higgs-Singlet extension of
the Standard Model. A fully automated procedure for the generation of
tree-level and one-loop matrix elements in general models, including
renormalization, is presented. We discuss the application of the
Background-Field Method to the extended models. Numerical results for NLO
electroweak cross sections are presented for different renormalization schemes
in the Two-Higgs-Doublet Model and the Higgs-Singlet extension of the Standard
Model. Finally, we present distributions for the production of a heavy Higgs
boson.Comment: 47 pages, 29 figures, pdflatex, version to appear in JHE
Efficient Color-Dressed Calculation of Virtual Corrections
With the advent of generalized unitarity and parametric integration
techniques, the construction of a generic Next-to-Leading Order Monte Carlo
becomes feasible. Such a generator will entail the treatment of QCD color in
the amplitudes. We extend the concept of color dressing to one-loop amplitudes,
resulting in the formulation of an explicit algorithmic solution for the
calculation of arbitrary scattering processes at Next-to-Leading order. The
resulting algorithm is of exponential complexity, that is the numerical
evaluation time of the virtual corrections grows by a constant multiplicative
factor as the number of external partons is increased. To study the properties
of the method, we calculate the virtual corrections to -gluon scattering.Comment: 48 pages, 23 figure
Optimization as a design strategy. Considerations based on building simulation-assisted experiments about problem decomposition
In this article the most fundamental decomposition-based optimization method
- block coordinate search, based on the sequential decomposition of problems in
subproblems - and building performance simulation programs are used to reason
about a building design process at micro-urban scale and strategies are defined
to make the search more efficient. Cyclic overlapping block coordinate search
is here considered in its double nature of optimization method and surrogate
model (and metaphore) of a sequential design process. Heuristic indicators apt
to support the design of search structures suited to that method are developed
from building-simulation-assisted computational experiments, aimed to choose
the form and position of a small building in a plot. Those indicators link the
sharing of structure between subspaces ("commonality") to recursive
recombination, measured as freshness of the search wake and novelty of the
search moves. The aim of these indicators is to measure the relative
effectiveness of decomposition-based design moves and create efficient block
searches. Implications of a possible use of these indicators in genetic
algorithms are also highlighted.Comment: 48 pages. 12 figures, 3 table
The Fibonacci scheme for fault-tolerant quantum computation
We rigorously analyze Knill's Fibonacci scheme for fault-tolerant quantum
computation, which is based on the recursive preparation of Bell states
protected by a concatenated error-detecting code. We prove lower bounds on the
threshold fault rate of .67\times 10^{-3} for adversarial local stochastic
noise, and 1.25\times 10^{-3} for independent depolarizing noise. In contrast
to other schemes with comparable proved accuracy thresholds, the Fibonacci
scheme has a significantly reduced overhead cost because it uses postselection
far more sparingly.Comment: 24 pages, 10 figures; supersedes arXiv:0709.3603. (v2): Additional
discussion about the overhead cos
Design and implementation of the node identity internetworking architecture
The Internet Protocol (IP) has been proven very flexible, being able to accommodate all kinds of link technologies and supporting a broad range of applications. The basic principles of the original Internet architecture include end-to-end addressing, global routeability and a single namespace of IP addresses that unintentionally serves both as locators and host identifiers. The commercial success and widespread use of the Internet have lead to new requirements, which include internetworking over business boundaries, mobility and multi-homing in an untrusted environment. Our approach to satisfy these new requirements is to introduce a new internetworking layer, the node identity layer. Such a layer runs on top of the different versions of IP, but could also run directly on top of other kinds of network technologies, such as MPLS and 2G/3G PDP contexts. This approach enables connectivity across different communication technologies, supports mobility, multi-homing, and security from ground up. This paper describes the Node Identity Architecture in detail and discusses the experiences from implementing and running a prototype
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