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Using formal methods to support testing
Formal methods and testing are two important approaches that assist in the development of high quality software. While traditionally these approaches have been seen as rivals, in recent
years a new consensus has developed in which they are seen as complementary. This article reviews the state of the art regarding ways in which the presence of a formal specification can be used to assist testing
Searching for Globally Optimal Functional Forms for Inter-Atomic Potentials Using Parallel Tempering and Genetic Programming
We develop a Genetic Programming-based methodology that enables discovery of
novel functional forms for classical inter-atomic force-fields, used in
molecular dynamics simulations. Unlike previous efforts in the field, that fit
only the parameters to the fixed functional forms, we instead use a novel
algorithm to search the space of many possible functional forms. While a
follow-on practical procedure will use experimental and {\it ab inito} data to
find an optimal functional form for a forcefield, we first validate the
approach using a manufactured solution. This validation has the advantage of a
well-defined metric of success. We manufactured a training set of atomic
coordinate data with an associated set of global energies using the well-known
Lennard-Jones inter-atomic potential. We performed an automatic functional form
fitting procedure starting with a population of random functions, using a
genetic programming functional formulation, and a parallel tempering
Metropolis-based optimization algorithm. Our massively-parallel method
independently discovered the Lennard-Jones function after searching for several
hours on 100 processors and covering a miniscule portion of the configuration
space. We find that the method is suitable for unsupervised discovery of
functional forms for inter-atomic potentials/force-fields. We also find that
our parallel tempering Metropolis-based approach significantly improves the
optimization convergence time, and takes good advantage of the parallel cluster
architecture
Extending Nunchaku to Dependent Type Theory
Nunchaku is a new higher-order counterexample generator based on a sequence
of transformations from polymorphic higher-order logic to first-order logic.
Unlike its predecessor Nitpick for Isabelle, it is designed as a stand-alone
tool, with frontends for various proof assistants. In this short paper, we
present some ideas to extend Nunchaku with partial support for dependent types
and type classes, to make frontends for Coq and other systems based on
dependent type theory more useful.Comment: In Proceedings HaTT 2016, arXiv:1606.0542
A survey on modeling of microgrids - from fundamental physics to phasors and voltage sources
Microgrids have been identified as key components of modern electrical
systems to facilitate the integration of renewable distributed generation
units. Their analysis and controller design requires the development of
advanced (typically model-based) techniques naturally posing an interesting
challenge to the control community. Although there are widely accepted reduced
order models to describe the dynamic behavior of microgrids, they are typically
presented without details about the reduction procedure---hampering the
understanding of the physical phenomena behind them. Preceded by an
introduction to basic notions and definitions in power systems, the present
survey reviews key characteristics and main components of a microgrid. We
introduce the reader to the basic functionality of DC/AC inverters, as well as
to standard operating modes and control schemes of inverter-interfaced power
sources in microgrid applications. Based on this exposition and starting from
fundamental physics, we present detailed dynamical models of the main microgrid
components. Furthermore, we clearly state the underlying assumptions which lead
to the standard reduced model with inverters represented by controllable
voltage sources, as well as static network and load representations, hence,
providing a complete modular model derivation of a three-phase inverter-based
microgrid
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