92,335 research outputs found
An automatic adaptive method to combine summary statistics in approximate Bayesian computation
To infer the parameters of mechanistic models with intractable likelihoods,
techniques such as approximate Bayesian computation (ABC) are increasingly
being adopted. One of the main disadvantages of ABC in practical situations,
however, is that parameter inference must generally rely on summary statistics
of the data. This is particularly the case for problems involving
high-dimensional data, such as biological imaging experiments. However, some
summary statistics contain more information about parameters of interest than
others, and it is not always clear how to weight their contributions within the
ABC framework. We address this problem by developing an automatic, adaptive
algorithm that chooses weights for each summary statistic. Our algorithm aims
to maximize the distance between the prior and the approximate posterior by
automatically adapting the weights within the ABC distance function.
Computationally, we use a nearest neighbour estimator of the distance between
distributions. We justify the algorithm theoretically based on properties of
the nearest neighbour distance estimator. To demonstrate the effectiveness of
our algorithm, we apply it to a variety of test problems, including several
stochastic models of biochemical reaction networks, and a spatial model of
diffusion, and compare our results with existing algorithms
Automatic Metadata Generation using Associative Networks
In spite of its tremendous value, metadata is generally sparse and
incomplete, thereby hampering the effectiveness of digital information
services. Many of the existing mechanisms for the automated creation of
metadata rely primarily on content analysis which can be costly and
inefficient. The automatic metadata generation system proposed in this article
leverages resource relationships generated from existing metadata as a medium
for propagation from metadata-rich to metadata-poor resources. Because of its
independence from content analysis, it can be applied to a wide variety of
resource media types and is shown to be computationally inexpensive. The
proposed method operates through two distinct phases. Occurrence and
co-occurrence algorithms first generate an associative network of repository
resources leveraging existing repository metadata. Second, using the
associative network as a substrate, metadata associated with metadata-rich
resources is propagated to metadata-poor resources by means of a discrete-form
spreading activation algorithm. This article discusses the general framework
for building associative networks, an algorithm for disseminating metadata
through such networks, and the results of an experiment and validation of the
proposed method using a standard bibliographic dataset
Gene expression programming approach to event selection in high energy physics
Gene Expression Programming is a new evolutionary algorithm that overcomes many limitations of the more established Genetic Algorithms and Genetic Programming. Its first application to high energy physics data analysis is presented. The algorithm was successfully used for event selection on samples with both low and high background level. It allowed automatic identification of selection rules that can be interpreted as cuts applied on the input variables. The signal/background classification accuracy was over 90% in all cases
A Domain-Specific Language and Editor for Parallel Particle Methods
Domain-specific languages (DSLs) are of increasing importance in scientific
high-performance computing to reduce development costs, raise the level of
abstraction and, thus, ease scientific programming. However, designing and
implementing DSLs is not an easy task, as it requires knowledge of the
application domain and experience in language engineering and compilers.
Consequently, many DSLs follow a weak approach using macros or text generators,
which lack many of the features that make a DSL a comfortable for programmers.
Some of these features---e.g., syntax highlighting, type inference, error
reporting, and code completion---are easily provided by language workbenches,
which combine language engineering techniques and tools in a common ecosystem.
In this paper, we present the Parallel Particle-Mesh Environment (PPME), a DSL
and development environment for numerical simulations based on particle methods
and hybrid particle-mesh methods. PPME uses the meta programming system (MPS),
a projectional language workbench. PPME is the successor of the Parallel
Particle-Mesh Language (PPML), a Fortran-based DSL that used conventional
implementation strategies. We analyze and compare both languages and
demonstrate how the programmer's experience can be improved using static
analyses and projectional editing. Furthermore, we present an explicit domain
model for particle abstractions and the first formal type system for particle
methods.Comment: Submitted to ACM Transactions on Mathematical Software on Dec. 25,
201
GRACE at ONE-LOOP: Automatic calculation of 1-loop diagrams in the electroweak theory with gauge parameter independence checks
We describe the main building blocks of a generic automated package for the
calculation of Feynman diagrams. These blocks include the generation and
creation of a model file, the graph generation, the symbolic calculation at an
intermediate level of the Dirac and tensor algebra, implementation of the loop
integrals, the generation of the matrix elements or helicity amplitudes,
methods for the phase space integrations and eventually the event generation.
The report focuses on the fully automated systems for the calculation of
physical processes based on the experience in developing GRACE-loop. As such, a
detailed description of the renormalisation procedure in the Standard Model is
given emphasizing the central role played by the non-linear gauge fixing
conditions for the construction of such automated codes. The need for such
gauges is better appreciated when it comes to devising efficient and powerful
algorithms for the reduction of the tensorial structures of the loop integrals.
A new technique for these reduction algorithms is described. Explicit formulae
for all two-point functions in a generalised non-linear gauge are given,
together with the complete set of counterterms. We also show how infrared
divergences are dealt with in the system. We give a comprehensive presentation
of some systematic test-runs which have been performed at the one-loop level
for a wide variety of two-to-two processes to show the validity of the gauge
check. These cover fermion-fermion scattering, gauge boson scattering into
fermions, gauge bosons and Higgs bosons scattering processes. Comparisons with
existing results on some one-loop computation in the Standard Model show
excellent agreement. We also briefly recount some recent development concerning
the calculation of mutli-leg one-loop corrections.Comment: 131 pages. Manuscript expanded quite substantially with the inclusion
of an overview of automatic systems for the calculation of Feynman diagrams
both at tree-level and one-loop. Other additions include issues of
regularisation, width effects and renormalisation with unstable particles and
reduction of 5- and 6-point functions. This is a preprint version, final
version to appear as a Phys. Re
MC-TESTER v. 1.23: a universal tool for comparisons of Monte Carlo predictions for particle decays in high energy physics
Theoretical predictions in high energy physics are routinely provided in the
form of Monte Carlo generators. Comparisons of predictions from different
programs and/or different initialization set-ups are often necessary. MC-TESTER
can be used for such tests of decays of intermediate states (particles or
resonances) in a semi-automated way.
Since 2002 new functionalities were introduced into the package. In
particular, it now works with the HepMC event record, the standard for C++
programs. The complete set-up for benchmarking the interfaces, such as
interface between tau-lepton production and decay, including QED bremsstrahlung
effects is shown. The example is chosen to illustrate the new options
introduced into the program. From the technical perspective, our paper
documents software updates and supplements previous documentation.
As in the past, our test consists of two steps. Distinct Monte Carlo programs
are run separately; events with decays of a chosen particle are searched, and
information is stored by MC-TESTER. Then, at the analysis step, information
from a pair of runs may be compared and represented in the form of tables and
plots.
Updates introduced in the progam up to version 1.24.3 are also documented. In
particular, new configuration scripts or script to combine results from
multitude of runs into single information file to be used in analysis step are
explained.Comment: 27 pages 4 figure
Branching diffusion representation of semilinear PDEs and Monte Carlo approximation
We provide a representation result of parabolic semi-linear PD-Es, with
polynomial nonlinearity, by branching diffusion processes. We extend the
classical representation for KPP equations, introduced by Skorokhod (1964),
Watanabe (1965) and McKean (1975), by allowing for polynomial nonlinearity in
the pair , where is the solution of the PDE with space gradient
. Similar to the previous literature, our result requires a non-explosion
condition which restrict to "small maturity" or "small nonlinearity" of the
PDE. Our main ingredient is the automatic differentiation technique as in Henry
Labordere, Tan and Touzi (2015), based on the Malliavin integration by parts,
which allows to account for the nonlinearities in the gradient. As a
consequence, the particles of our branching diffusion are marked by the nature
of the nonlinearity. This new representation has very important numerical
implications as it is suitable for Monte Carlo simulation. Indeed, this
provides the first numerical method for high dimensional nonlinear PDEs with
error estimate induced by the dimension-free Central limit theorem. The
complexity is also easily seen to be of the order of the squared dimension. The
final section of this paper illustrates the efficiency of the algorithm by some
high dimensional numerical experiments
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