4,245 research outputs found
Elements of Design for Containers and Solutions in the LinBox Library
We describe in this paper new design techniques used in the \cpp exact linear
algebra library \linbox, intended to make the library safer and easier to use,
while keeping it generic and efficient. First, we review the new simplified
structure for containers, based on our \emph{founding scope allocation} model.
We explain design choices and their impact on coding: unification of our matrix
classes, clearer model for matrices and submatrices, \etc Then we present a
variation of the \emph{strategy} design pattern that is comprised of a
controller--plugin system: the controller (solution) chooses among plug-ins
(algorithms) that always call back the controllers for subtasks. We give
examples using the solution \mul. Finally we present a benchmark architecture
that serves two purposes: Providing the user with easier ways to produce
graphs; Creating a framework for automatically tuning the library and
supporting regression testing.Comment: 8 pages, 4th International Congress on Mathematical Software, Seoul :
Korea, Republic Of (2014
Hilbert-Post completeness for the state and the exception effects
In this paper, we present a novel framework for studying the syntactic
completeness of computational effects and we apply it to the exception effect.
When applied to the states effect, our framework can be seen as a
generalization of Pretnar's work on this subject. We first introduce a relative
notion of Hilbert-Post completeness, well-suited to the composition of effects.
Then we prove that the exception effect is relatively Hilbert-Post complete, as
well as the "core" language which may be used for implementing it; these proofs
have been formalized and checked with the proof assistant Coq.Comment: Siegfried Rump (Hamburg University of Technology), Chee Yap (Courant
Institute, NYU). Sixth International Conference on Mathematical Aspects of
Computer and Information Sciences , Nov 2015, Berlin, Germany. 2015, LNC
Combined quantum state preparation and laser cooling of a continuous beam of cold atoms
We use two-laser optical pumping on a continuous atomic fountain in order to
prepare cold cesium atoms in the same quantum ground state. A first laser
excites the F=4 ground state to pump the atoms toward F=3 while a second
pi-polarized laser excites the F=3 -> F'=3 transition of the D2 line to produce
Zeeman pumping toward m=0. To avoid trap states, we implement the first laser
in a 2D optical lattice geometry, thereby creating polarization gradients. This
configuration has the advantage of simultaneously producing Sisyphus cooling
when the optical lattice laser is tuned between the F=4 -> F'=4 and F=4 -> F'=5
transitions of the D2 line, which is important to remove the heat produced by
optical pumping. Detuning the frequency of the second pi-polarized laser
reveals the action of a new mechanism improving both laser cooling and state
preparation efficiency. A physical interpretation of this mechanism is
discussed.Comment: Minor changes according to the recommendations of the referee: -
Corrected Fig.1. - Split the graph of Fig.6 for clarity. - Added one
reference. - Added two remarks in the conclusion. - Results unchange
Observation of correlations up to the micrometer scale in sliding charge-density waves
High-resolution coherent x-ray diffraction experiment has been performed on
the charge density wave (CDW) system KMoO. The satellite
reflection associated with the CDW has been measured with respect to external
dc currents. In the sliding regime, the satellite reflection displays
secondary satellites along the chain axis which corresponds to correlations up
to the micrometer scale. This super long range order is 1500 times larger than
the CDW period itself. This new type of electronic correlation seems inherent
to the collective dynamics of electrons in charge density wave systems. Several
scenarios are discussed.Comment: 4 pages, 3 figures Typos added, references remove
Parallel computation of echelon forms
International audienceWe propose efficient parallel algorithms and implementations on shared memory architectures of LU factorization over a finite field. Compared to the corresponding numerical routines, we have identified three main difficulties specific to linear algebra over finite fields. First, the arithmetic complexity could be dominated by modular reductions. Therefore, it is mandatory to delay as much as possible these reductions while mixing fine-grain parallelizations of tiled iterative and recursive algorithms. Second, fast linear algebra variants, e.g., using Strassen-Winograd algorithm, never suffer from instability and can thus be widely used in cascade with the classical algorithms. There, trade-offs are to be made between size of blocks well suited to those fast variants or to load and communication balancing. Third, many applications over finite fields require the rank profile of the matrix (quite often rank deficient) rather than the solution to a linear system. It is thus important to design parallel algorithms that preserve and compute this rank profile. Moreover, as the rank profile is only discovered during the algorithm, block size has then to be dynamic. We propose and compare several block decomposition: tile iterative with left-looking, right-looking and Crout variants, slab and tile recursive. Experiments demonstrate that the tile recursive variant performs better and matches the performance of reference numerical software when no rank deficiency occur. Furthermore, even in the most heterogeneous case, namely when all pivot blocks are rank deficient, we show that it is possbile to maintain a high efficiency
A survey of young, nearby, and dusty stars to understand the formation of wide-orbit giant planets
Direct imaging has confirmed the existence of substellar companions on wide
orbits. To understand the formation and evolution mechanisms of these
companions, the full population properties must be characterized. We aim at
detecting giant planet and/or brown dwarf companions around young, nearby, and
dusty stars. Our goal is also to provide statistics on the population of giant
planets at wide-orbits and discuss planet formation models. We report a deep
survey of 59 stars, members of young stellar associations. The observations
were conducted with VLT/NaCo at L'-band (3.8 micron). We used angular
differential imaging to reach optimal detection performance. A statistical
analysis of about 60 % of the young and southern A-F stars closer than 65 pc
allows us to derive the fraction of giant planets on wide orbits. We use
gravitational instability models and planet population synthesis models
following the core-accretion scenario to discuss the occurrence of these
companions. We resolve and characterize new visual binaries and do not detect
any new substellar companion. The survey's median detection performance reaches
contrasts of 10 mag at 0.5as and 11.5 mag at 1as. We find the occurrence of
planets to be between 10.8-24.8 % at 68 % confidence level assuming a uniform
distribution of planets in the interval 1-13 Mj and 1-1000 AU. Considering the
predictions of formation models, we set important constraints on the occurrence
of massive planets and brown dwarf companions that would have formed by GI. We
show that this mechanism favors the formation of rather massive clump (Mclump >
30 Mj) at wide (a > 40 AU) orbits which might evolve dynamically and/or
fragment. For the population of close-in giant planets that would have formed
by CA, our survey marginally explore physical separations (<20 AU) and cannot
constrain this population
Recursive double-size fixed precision arithmetic
International audienceThis work is a part of the SHIVA (Secured Hardware Immune Versatile Architecture) project whose purpose is to provide a programmable and reconfigurable hardware module with high level of security. We propose a recursive double-size fixed precision arithmetic called RecInt. Our work can be split in two parts. First we developped a C++ software library with performances comparable to GMP ones. Secondly our simple representation of the integers allows an implementation on FPGA. Our idea is to consider sizes that are a power of 2 and to apply doubling techniques to implement them efficiently: we design a recursive data structure where integers of size 2^k, for k>k0 can be stored as two integers of size 2^{k-1}. Obviously for k<=k0 we use machine arithmetic instead (k0 depending on the architecture)
Type II Shocks Characteristics: Comparison with associated CMEs and Flares
A number of metric (100-650 MHz) typeII bursts was recorded by the ARTEMIS-IV
radiospectrograph in the 1998-2000 period; the sample includes both CME driven
shocks and shocks originating from flare blasts. We study their characteristics
in comparison with characteristics of associated CMEs and flares.Comment: Recent Advances in Astronomy and Astrophysics: 7th International
Conference of the Hellenic Astronomical Society. AIP Conference Proceedings,
Volume 848, pp. 238-242 (2006
Type II and IV radio bursts in the active period October-November 2003
In this report we present the Type II and IV radio bursts observed and
analyzed by the radio spectrograph ARTEMIS IV1, in the 650-20MHz frequency
range, during the active period October-November 2003. These bursts exhibit
very rich fine structures such fibers, pulsations and zebra patterns which is
associated with certain characteristics of the associated solar flares and
CMEs.Comment: Recent Advances in Astronomy and Astrophysics: 7th International
Conference of the Hellenic Astronomical Society. AIP Conference Proceedings,
Volume 848, pp. 199-206 (2006
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