73,708 research outputs found
Incremental and Modular Context-sensitive Analysis
Context-sensitive global analysis of large code bases can be expensive, which
can make its use impractical during software development. However, there are
many situations in which modifications are small and isolated within a few
components, and it is desirable to reuse as much as possible previous analysis
results. This has been achieved to date through incremental global analysis
fixpoint algorithms that achieve cost reductions at fine levels of granularity,
such as changes in program lines. However, these fine-grained techniques are
not directly applicable to modular programs, nor are they designed to take
advantage of modular structures. This paper describes, implements, and
evaluates an algorithm that performs efficient context-sensitive analysis
incrementally on modular partitions of programs. The experimental results show
that the proposed modular algorithm shows significant improvements, in both
time and memory consumption, when compared to existing non-modular, fine-grain
incremental analysis techniques. Furthermore, thanks to the proposed
inter-modular propagation of analysis information, our algorithm also
outperforms traditional modular analysis even when analyzing from scratch.Comment: 56 pages, 27 figures. To be published in Theory and Practice of Logic
Programming. v3 corresponds to the extended version of the ICLP2018 Technical
Communication. v4 is the revised version submitted to Theory and Practice of
Logic Programming. v5 (this one) is the final author version to be published
in TPL
Coding Theory and Algebraic Combinatorics
This chapter introduces and elaborates on the fruitful interplay of coding
theory and algebraic combinatorics, with most of the focus on the interaction
of codes with combinatorial designs, finite geometries, simple groups, sphere
packings, kissing numbers, lattices, and association schemes. In particular,
special interest is devoted to the relationship between codes and combinatorial
designs. We describe and recapitulate important results in the development of
the state of the art. In addition, we give illustrative examples and
constructions, and highlight recent advances. Finally, we provide a collection
of significant open problems and challenges concerning future research.Comment: 33 pages; handbook chapter, to appear in: "Selected Topics in
Information and Coding Theory", ed. by I. Woungang et al., World Scientific,
Singapore, 201
Primitive decompositions of Johnson graphs
A transitive decomposition of a graph is a partition of the edge set together
with a group of automorphisms which transitively permutes the parts. In this
paper we determine all transitive decompositions of the Johnson graphs such
that the group preserving the partition is arc-transitive and acts primitively
on the parts.Comment: 35 page
A GPU-Enabled, High-Resolution Cosmological Microlensing Parameter Survey
In the era of synoptic surveys, the number of known gravitationally lensed
quasars is set to increase by over an order of magnitude. These new discoveries
will enable a move from single-quasar studies to investigations of statistical
samples, presenting new opportunities to test theoretical models for the
structure of quasar accretion discs and broad emission line regions (BELRs). As
one crucial step in preparing for this influx of new lensed systems, a
large-scale exploration of microlensing convergence-shear parameter space is
warranted, requiring the computation of O(10^5) high resolution magnification
maps. Based on properties of known lensed quasars, and expectations from
accretion disc/BELR modelling, we identify regions of convergence-shear
parameter space, map sizes, smooth matter fractions, and pixel resolutions that
should be covered. We describe how the computationally time-consuming task of
producing ~290000 magnification maps with sufficient resolution (10000^2
pixel/map) to probe scales from the inner edge of the accretion disc to the
BELR can be achieved in ~400 days on a 100 teraflop/s high performance
computing facility, where the processing performance is achieved with graphics
processing units. We illustrate a use-case for the parameter survey by
investigating the effects of varying the lens macro-model on accretion disc
constraints in the lensed quasar Q2237+0305. We find that although all
constraints are consistent within their current error bars, models with more
densely packed microlenses tend to predict shallower accretion disc radial
temperature profiles. With a large parameter survey such as the one described
here, such systematics on microlensing measurements could be fully explored.Comment: 30 pages, 3 figures, accepted for publication in Ap
The 3-Dimensional Distribution of Dust in NGC 891
We produce three-dimensional Monte-Carlo radiative transfer models of the
edge-on spiral galaxy NGC 891, a fast-rotating galaxy thought to be an analogue
to the Milky Way. The models contain realistic spiral arms and a fractal
distribution of clumpy dust. We fit our models to Hubble Space Telescope images
corresponding to the B and I bands, using shapelet analysis and a genetic
algorithm to generate 30 statistically best-fitting models. These models have a
strong preference for spirality and clumpiness, with average face-on
attenuation decreasing from 0.24(0.16) to 0.03(0.03) mag in the B(I) band
between 0.5 and 2 radial scale-lengths. Most of the attenuation comes from
small high-density clumps with low (<10%) filling factors. The fraction of dust
in clumps is broadly consistent with results from fitting NGC 891's spectral
energy distribution. Because of scattering effects and the intermixed nature of
the dust and starlight, attenuation is smaller and less wavelength-dependent
than the integrated dust column-density. Our clumpy models typically have
higher attenuation at low inclinations than previous radiative transfer models
using smooth distributions of stars and dust, but similar attenuation at
inclinations above 70 degrees. At all inclinations most clumpy models have less
attenuation than expected from previous estimates based on minimizing scatter
in the Tully-Fisher relation. Mass-to-light ratios are higher and the intrinsic
scatter in the Tully-Fisher relation is larger than previously expected for
galaxies similar to NGC 891. The attenuation curve changes as a function of
inclination, with R_(B,B-I)=A_(B)/E(B-I) increasing by ~0.75 from face-on to
near-edge-on orientations.Comment: 26 pages, 18 figures, accepted for publication in Ap
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