198 research outputs found
Stack graphs: Name resolution at scale
We present stack graphs, an extension of Visser et al.'s scope graphs
framework. Stack graphs power Precise Code Navigation at GitHub, allowing users
to navigate name binding references both within and across repositories. Like
scope graphs, stack graphs encode the name binding information about a program
in a graph structure, in which paths represent valid name bindings. Resolving a
reference to its definition is then implemented with a simple path-finding
search.
GitHub hosts millions of repositories, containing petabytes of total code,
implemented in hundreds of different programming languages, and receiving
thousands of pushes per minute. To support this scale, we update the graph
construction and path-finding judgments to be file-incremental. For each source
file, we create an isolated subgraph without any knowledge of, or visibility
into, any other file in the program. This lets us eliminate the storage and
compute costs of reanalyzing file versions that we have already seen. Since
most commits change a small fraction of the files in a repository, this greatly
amortizes the operational costs of indexing large, frequently changed
repositories over time. To handle type-directed name lookups (which require
"pausing" the current lookup to resolve another name), our path-finding
algorithm maintains a stack of the currently paused (but still pending)
lookups. Stack graphs can be constructed via a purely syntactic analysis of the
program's source code, using a new declarative graph construction language.
This means that we can extract name binding information for every repository
without any per-package configuration, and without having to invoke an
arbitrary, untrusted, package-specific build process.Comment: 8 pages, submitted to Eelco Visser Commemorative Symposium 202
Nilpotency of skew braces and multipermutation solutions of the Yang-Baxter equation
We study relations between different notions of nilpotency in the context of
skew braces and applications to the structure of solutions to the Yang-Baxter
equation. In particular, we consider annihilator nilpotent skew braces, an
important class that turns out to be a brace-theoretic analog to the class of
nilpotent groups. In this vein, several well-known theorems in group theory are
proved in the more general setting of skew braces.Comment: 18 pages. Postprint versio
Factorizations of skew braces
We introduce strong left ideals of skew braces and prove that they produce non-trivial decomposition of set-theoretic solutions of the YangâBaxter equation. We study factorization of skew left braces through strong left ideals and we prove analogs of ItĂŽâs theorem in the context of skew left braces. As a corollary, we obtain applications to the retractability problem of involutive non-degenerate solutions of the YangâBaxter equation. Finally, we classify skew braces that contain no non-trivial proper characteristic ideals.Fil: Jespers, E.. Vrije Unviversiteit Brussel; BĂ©lgicaFil: Kubat, L.. Vrije Unviversiteit Brussel; BĂ©lgicaFil: Van Antwerpen, A.. Vrije Unviversiteit Brussel; BĂ©lgicaFil: Vendramin, Claudio Leandro. Institute of Mathematical Sciences at NYU Shanghai; China. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
On various types of nilpotency of the structure monoid and group of a set-theoretic solution of the Yang--Baxter equation
Given a finite bijective non-degenerate set-theoretic solution of the
Yang--Baxter equation we characterize when its structure monoid is
Malcev nilpotent. Applying this characterization to solutions coming from
racks, we rediscover some results obtained recently by Lebed and Mortier, and
by Lebed and Vendramin on the description of finite abelian racks and quandles.
We also investigate bijective non-degenerate multipermutation (not
necessarily finite) solutions and show, for example, that this property
is equivalent to the solution associated to the structure monoid
(respectively structure group ) being a multipermuation solution and
that is solvable of derived length not exceeding the
multipermutation level of enlarged by one, generalizing results of
Gateva-Ivanova and Cameron obtained in the involutive case. Moreover, we also
prove that if is finite and is nilpotent, then the torsion part
of the group is finite, it coincides with the commutator subgroup
of the additive structure of the skew left brace and is a
trivial left brace.Comment: 35 page
Consultancy haalbaarheid Klimrekscherm
Deze haalbaarheidstudie heeft als doel de mogelijkheden van het klimrek systeem in de glastuinbouw in kaart te brengen in een semi-gesloten teelt concept teneinde te komen tot energiebesparing, productieverhoging, betere kwaliteit, betere CO2 benutting en minder uitval ten gevolge van vochtproblemen door een te hoge RV
Higgs boson as a gluon trigger: the study of QCD in high pile-up environments
In the forthcoming high-luminosity phase of the LHC many of the most
interesting measurements for precision QCD studies are hampered by large
pile-up conditions, especially at not very high transverse momenta. However,
with the recently discovered Higgs boson, which couples in the heavy top limit
directly to gluons, we have access to a novel production process to probe QCD
by a colour-singlet current. In this study we compare observables in Higgs
boson and Drell-Yan production and investigate whether measuring ratios or
subtractions can yield results that are stable in high pile-up environments,
and yet sensitive to (small-) QCD physics in gluon fusion
processes. We present results of Monte Carlo event generator calculations for a
few specific examples.Comment: 7 pages, 10 figures, DIS2014 conference proceeding
Gauging the three-nucleon spectator equation
We derive relativistic three-dimensional integral equations describing the
interaction of the three-nucleon system with an external electromagnetic field.
Our equations are unitary, gauge invariant, and they conserve charge. This has
been achieved by applying the recently introduced gauging of equations method
to the three-nucleon spectator equations where spectator nucleons are always on
mass shell. As a result, the external photon is attached to all possible places
in the strong interaction model, so that current and charge conservation are
implemented in the theoretically correct fashion. Explicit expressions are
given for the three-nucleon bound state electromagnetic current, as well as the
transition currents for the scattering processes
\gamma He3 -> NNN, Nd -> \gamma Nd, and \gamma He3 -> Nd. As a result, a
unified covariant three-dimensional description of the NNN-\gamma NNN system is
achieved.Comment: 23 pages, REVTeX, epsf, 4 Postscript figure
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