17,557 research outputs found
Computer-Assisted Program Reasoning Based on a Relational Semantics of Programs
We present an approach to program reasoning which inserts between a program
and its verification conditions an additional layer, the denotation of the
program expressed in a declarative form. The program is first translated into
its denotation from which subsequently the verification conditions are
generated. However, even before (and independently of) any verification
attempt, one may investigate the denotation itself to get insight into the
"semantic essence" of the program, in particular to see whether the denotation
indeed gives reason to believe that the program has the expected behavior.
Errors in the program and in the meta-information may thus be detected and
fixed prior to actually performing the formal verification. More concretely,
following the relational approach to program semantics, we model the effect of
a program as a binary relation on program states. A formal calculus is devised
to derive from a program a logic formula that describes this relation and is
subject for inspection and manipulation. We have implemented this idea in a
comprehensive form in the RISC ProgramExplorer, a new program reasoning
environment for educational purposes which encompasses the previously developed
RISC ProofNavigator as an interactive proving assistant.Comment: In Proceedings THedu'11, arXiv:1202.453
A Static Analyzer for Large Safety-Critical Software
We show that abstract interpretation-based static program analysis can be
made efficient and precise enough to formally verify a class of properties for
a family of large programs with few or no false alarms. This is achieved by
refinement of a general purpose static analyzer and later adaptation to
particular programs of the family by the end-user through parametrization. This
is applied to the proof of soundness of data manipulation operations at the
machine level for periodic synchronous safety critical embedded software. The
main novelties are the design principle of static analyzers by refinement and
adaptation through parametrization, the symbolic manipulation of expressions to
improve the precision of abstract transfer functions, the octagon, ellipsoid,
and decision tree abstract domains, all with sound handling of rounding errors
in floating point computations, widening strategies (with thresholds, delayed)
and the automatic determination of the parameters (parametrized packing)
Computer-assisted access to the kidney
OBJECTIVES: The aim of this paper is to introduce the principles of
computer-assisted access to the kidney. The system provides the surgeon with a
pre-operative 3D planning on computed tomography (CT) images. After a rigid
registration with space-localized ultrasound (US) data, preoperative planning
can be transferred to the intra-operative conditions and an intuitive
man-machine interface allows the user to perform a puncture. MATERIAL AND
METHODS: Both CT and US images of informed normal volunteer were obtained to
perform calculation on the accuracy of registration and punctures were carried
out on a kidney phantom to measure the precision of the whole of the system.
RESULTS: We carried out millimetric registrations on real data and guidance
experiments on a kidney phantom showed encouraging results of 4.7 mm between
planned and reached targets. We noticed that the most significant error was
related to the needle deflection during the puncture. CONCLUSION: Preliminary
results are encouraging. Further work will be undertaken to improve efficiency
and accuracy, and to take breathing into account
Resonance-Assisted Tunneling
We present evidence that tunneling processes in near-integrable systems are
enhanced due to the manifestation of nonlinear resonances and their respective
island chains in phase space. A semiclassical description of this
"resonance-assisted" mechanism is given, which is based on a local perturbative
description of the dynamics in the vicinity of the resonances. As underlying
picture, we obtain that the quantum state is coupled, via a succession of
classically forbidden transitions across nonlinear resonances, to high
excitations within the well, from where tunneling occurs with a rather large
rate. The connection between this description and the complex classical
structure of the underlying integrable dynamics is furthermore studied, giving
ground to the general coherence of the description as well as guidelines for
the identification of the dominant tunneling paths. The validity of this
mechanism is demonstrated within the kicked Harper model, where good agreement
between quantum and semiclassical (resonance-assisted) tunneling rates is
found.Comment: 52 pages, 16 figures, submitted to Annals of Physic
Indexed Labels for Loop Iteration Dependent Costs
We present an extension to the labelling approach, a technique for lifting
resource consumption information from compiled to source code. This approach,
which is at the core of the annotating compiler from a large fragment of C to
8051 assembly of the CerCo project, looses preciseness when differences arise
as to the cost of the same portion of code, whether due to code transformation
such as loop optimisations or advanced architecture features (e.g. cache). We
propose to address this weakness by formally indexing cost labels with the
iterations of the containing loops they occur in. These indexes can be
transformed during the compilation, and when lifted back to source code they
produce dependent costs.
The proposed changes have been implemented in CerCo's untrusted prototype
compiler from a large fragment of C to 8051 assembly.Comment: In Proceedings QAPL 2013, arXiv:1306.241
Towards an Observational Appraisal of String Cosmology
We review the current observational status of string cosmology when
confronted with experimental datasets. We begin by defining common
observational parameters and discuss how they are determined for a given model.
Then we review the observable footprints of several string theoretic models,
discussing the significance of various potential signals. Throughout we comment
on present and future prospects of finding evidence for string theory in
cosmology, and on significant issues for the future.Comment: Review accepted for publication in the CQG focus issue on string
cosmology. Minor clarifications and references adde
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