77,339 research outputs found
A short note on Simulation and Abstraction
This short note is written in celebration of David Schmidt's sixtieth
birthday. He has now been active in the program analysis research community for
over thirty years and we have enjoyed many interactions with him. His work on
characterising simulations between Kripke structures using Galois connections
was particularly influential in our own work on using probabilistic abstract
interpretation to study Larsen and Skou's notion of probabilistic bisimulation.
We briefly review this work and discuss some recent applications of these ideas
in a variety of different application areas.Comment: In Proceedings Festschrift for Dave Schmidt, arXiv:1309.455
Abstraction of Elementary Hybrid Systems by Variable Transformation
Elementary hybrid systems (EHSs) are those hybrid systems (HSs) containing
elementary functions such as exp, ln, sin, cos, etc. EHSs are very common in
practice, especially in safety-critical domains. Due to the non-polynomial
expressions which lead to undecidable arithmetic, verification of EHSs is very
hard. Existing approaches based on partition of state space or
over-approximation of reachable sets suffer from state explosion or inflation
of numerical errors. In this paper, we propose a symbolic abstraction approach
that reduces EHSs to polynomial hybrid systems (PHSs), by replacing all
non-polynomial terms with newly introduced variables. Thus the verification of
EHSs is reduced to the one of PHSs, enabling us to apply all the
well-established verification techniques and tools for PHSs to EHSs. In this
way, it is possible to avoid the limitations of many existing methods. We
illustrate the abstraction approach and its application in safety verification
of EHSs by several real world examples
Model checking learning agent systems using Promela with embedded C code and abstraction
As autonomous systems become more prevalent, methods for their verification will become more
widely used. Model checking is a formal verification technique that can help ensure the safety of autonomous
systems, but in most cases it cannot be applied by novices, or in its straight \off-the-shelf" form. In order
to be more widely applicable it is crucial that more sophisticated techniques are used, and are presented
in a way that is reproducible by engineers and verifiers alike. In this paper we demonstrate in detail two
techniques that are used to increase the power of model checking using the model checker SPIN. The first
of these is the use of embedded C code within Promela specifications, in order to accurately re
ect robot
movement. The second is to use abstraction together with a simulation relation to allow us to verify multiple
environments simultaneously. We apply these techniques to a fairly simple system in which a robot moves
about a fixed circular environment and learns to avoid obstacles. The learning algorithm is inspired by the
way that insects learn to avoid obstacles in response to pain signals received from their antennae. Crucially,
we prove that our abstraction is sound for our example system { a step that is often omitted but is vital if
formal verification is to be widely accepted as a useful and meaningful approach
A parallel multistate framework for atomistic non-equilibrium reaction dynamics of solutes in strongly interacting organic solvents
We describe a parallel linear-scaling computational framework developed to
implement arbitrarily large multi-state empirical valence bond (MS-EVB)
calculations within CHARMM. Forces are obtained using the Hellman-Feynmann
relationship, giving continuous gradients, and excellent energy conservation.
Utilizing multi-dimensional Gaussian coupling elements fit to CCSD(T)-F12
electronic structure theory, we built a 64-state MS-EVB model designed to study
the F + CD3CN -> DF + CD2CN reaction in CD3CN solvent. This approach allows us
to build a reactive potential energy surface (PES) whose balanced accuracy and
efficiency considerably surpass what we could achieve otherwise. We use our PES
to run MD simulations, and examine a range of transient observables which
follow in the wake of reaction, including transient spectra of the DF
vibrational band, time dependent profiles of vibrationally excited DF in CD3CN
solvent, and relaxation rates for energy flow from DF into the solvent, all of
which agree well with experimental observations. Immediately following
deuterium abstraction, the nascent DF is in a non-equilibrium regime in two
different respects: (1) it is highly excited, with ~23 kcal mol-1 localized in
the stretch; and (2) not yet Hydrogen bonded to the CD3CN solvent, its
microsolvation environment is intermediate between the non-interacting
gas-phase limit and the solution-phase equilibrium limit. Vibrational
relaxation of the nascent DF results in a spectral blue shift, while relaxation
of its microsolvation environment results in a red shift. These two competing
effects result in a post-reaction relaxation profile distinct from that
observed when DF vibration excitation occurs within an equilibrium
microsolvation environment. The parallel software framework presented in this
paper should be more broadly applicable to a range of complex reactive systems.Comment: 58 pages and 29 Figure
Reachability in Biochemical Dynamical Systems by Quantitative Discrete Approximation (extended abstract)
In this paper, a novel computational technique for finite discrete
approximation of continuous dynamical systems suitable for a significant class
of biochemical dynamical systems is introduced. The method is parameterized in
order to affect the imposed level of approximation provided that with
increasing parameter value the approximation converges to the original
continuous system. By employing this approximation technique, we present
algorithms solving the reachability problem for biochemical dynamical systems.
The presented method and algorithms are evaluated on several exemplary
biological models and on a real case study.Comment: In Proceedings CompMod 2011, arXiv:1109.104
Generalized Strong Preservation by Abstract Interpretation
Standard abstract model checking relies on abstract Kripke structures which
approximate concrete models by gluing together indistinguishable states, namely
by a partition of the concrete state space. Strong preservation for a
specification language L encodes the equivalence of concrete and abstract model
checking of formulas in L. We show how abstract interpretation can be used to
design abstract models that are more general than abstract Kripke structures.
Accordingly, strong preservation is generalized to abstract
interpretation-based models and precisely related to the concept of
completeness in abstract interpretation. The problem of minimally refining an
abstract model in order to make it strongly preserving for some language L can
be formulated as a minimal domain refinement in abstract interpretation in
order to get completeness w.r.t. the logical/temporal operators of L. It turns
out that this refined strongly preserving abstract model always exists and can
be characterized as a greatest fixed point. As a consequence, some well-known
behavioural equivalences, like bisimulation, simulation and stuttering, and
their corresponding partition refinement algorithms can be elegantly
characterized in abstract interpretation as completeness properties and
refinements
- …