Adjoint computations by algorithmic differentiation of a parallel solver for time-dependent PDEs

A computational fluid dynamics code is differentiated using algorithmic differentiation (AD) in both tangent and adjoint modes. The two novelties of the present approach are 1) the adjoint code is obtained by letting the AD tool Tapenade invert the complete layer of message passing interface (MPI) communications, and 2) the adjoint code integrates time-dependent, non-linear and dissipative (hence physically irreversible) PDEs with an explicit time integration loop running for ca. $10^{6}$ time steps. The approach relies on using the Adjoinable MPI library to reverse the non-blocking communication patterns in the original code, and by controlling the memory overhead induced by the time-stepping loop with binomial checkpointing. A description of the necessary code modifications is provided along with the validation of the computed derivatives and a performance comparison of the tangent and adjoint codes.Comment: Submitted to Journal of Computational Scienc

How universal is the fractional-quantum-Hall edge Luttinger liquid?

This article reports on our microscopic investigations of the edge of the fractional quantum Hall state at filling factor $\nu=1/3$. We show that the interaction dependence of the wave function is well described in an approximation that includes mixing with higher composite-fermion Landau levels in the lowest order. We then proceed to calculate the equal time edge Green function, which provides evidence that the Luttinger exponent characterizing the decay of the Green function at long distances is interaction dependent. The relevance of this result to tunneling experiments is discussed.Comment: 5 page

Automatic Differentiation Adjoint of the Reynolds-Averaged Navier-Stokes Equations with a Turbulence Model

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106452/1/AIAA2013-2581.pd

AD-based perturbation methods for uncertainties and errors

International audienceThe progress of Automatic Differentiation ({\bf AD}) and its impact on perturbation methods is the object of this paper. AD studies show an important activity for developing methods addressing the management of modern CFD kernels, taking into account the language evolution, and intensive parallel computing. The evaluation of a posteriori error analysis and of resulting correctors will be addressed. Recents works in the AD-based contruction of second-derivatives for building reduced-order models based on a Taylor formula will be presented on the test case of a steady compressible flow around an aircraft

Was the "naked burst" GRB 050421 really naked ?

A few long gamma-ray bursts such as GRB 050421 show no afterglow emission beyond the usual initial steep decay phase. It has been suggested that these events correspond to "naked" bursts that occur in a very low density environment. We reconsider this possibility in the context of various scenarios for the origin of the afterglow. In the standard model where the afterglow results from the forward shock as well as in the alternative model where the afterglow comes from the reverse shock, we aim to obtain constraints on the density of the environment, the microphysics parameters, or the Lorentz factor of the ejecta, which are imposed by the absence of a detected afterglow. For the two models we compute the afterglow evolution for different values of the external density (uniform or wind medium) and various burst parameters. We then compare our results to the Swift data of GRB 050421, which is the best example of a long burst without afterglow. In the standard model we show that consistency with the data imposes that the external density does not exceed 1E-5 cm-3 or that the microphysics parameters are very small with epsilon_e <~ 1E-2 and epsilon_B <~ 1E-4. If the afterglow is caused by the reverse shock, we find that its contribution can be strongly reduced if the central source has mainly emitted fast-moving material (with less than 10 - 30 % of the kinetic energy at Gamma<100 and was located in a dense environment. The two considered scenarios therefore lead to opposite constraints on the circumburst medium. The high-density environment, favored by the reverse shock model, better corresponds to what is expected if the burst progenitor was a massive star.Comment: 6 pages, 3 figures, 1 table, to appear in A&

Stents in pediatric and adult congenital cardiac catheterization in France in 2013

Stents have contributed to the development of the interventional catheterization for congenital heart diseases (CHD). The aim of this study was to describe indications, results and adverse events in current practice.MethodsThe participation to this study was proposed to all catheterization laboratories specialized in CHD in France (M3C network). All cases with stents implantation in 2013 in pediatric and adult CHD were retrospectively included. Adverse events were assessed using the Bergersen classification.Results174 stents were implanted during 132 procedures in 127 patients by 6 main operators in 9 centers. Patients were aged 15.7±15.1years old (min 5day-old - max 70years old). Sixteen types of procedures were identified. Main indications were transcatheter pulmonary valve replacement (29 patients, 23.0%), pulmonary artery branches angioplasty (34 patients, 27.0%), aortic (re)coarctation stenting (37 patients, 29.4%) and ductus arteriosus stenting (11 patients, 8.7%). 18 patients (14.3%) were under one y.o and 35 (27.8%) were over 18y.o. Main pathologies were tetralogy of Fallot and variants (ACC-CHD 8.3, n=45, 35.7%), and aortic coarctation (ACC-CHD 9.2, n=36, 28.6%). More than 1 stent was implanted in 32 procedures (24.4%, max. 5 stents). Main stents implanted were the CP stent (33.0%), EV3 LD max (22.0%), Valeo (16.2%) and valved stents (15.0%). 98.5% procedures were considered as successful. Serious adverse events were observed in 12.9%. After multivariate adjustment, only procedure type was related to the risk of total adverse events (OR: 3.0, 95%CI 1.1–7.9) but not to stent related adverse events. Age, weight, center, operator, type of stents, stent diameter, genetic disorder and type of CHD were not significantly related to the risk of adverse events.ConclusionStents are used in various CHD catheterization procedures, from infancy to adult age. Adverse events rate is significant and seems related to the type of procedure

MCMC for Bayesian uncertainty quantification from time-series data

In computational neuroscience, Neural Population Models (NPMs) are mechanistic models that describe brain physiology in a range of different states. Within computational neuroscience there is growing interest in the inverse problem of inferring NPM parameters from recordings such as the EEG (Electroencephalogram). Uncertainty quantification is essential in this application area in order to infer the mechanistic effect of interventions such as anaesthesia. This paper presents Open image in new window software for Bayesian uncertainty quantification in the parameters of NPMs from approximately stationary data using Markov Chain Monte Carlo (MCMC). Modern MCMC methods require first order (and in some cases higher order) derivatives of the posterior density. The software presented offers two distinct methods of evaluating derivatives: finite differences and exact derivatives obtained through Algorithmic Differentiation (AD). For AD, two different implementations are used: the open source Stan Math Library and the commercially licenced Open image in new window tool distributed by NAG (Numerical Algorithms Group). The use of derivative information in MCMC sampling is demonstrated through a simple example, the noise-driven harmonic oscillator. And different methods for computing derivatives are compared. The software is written in a modular object-oriented way such that it can be extended to derivative based MCMC for other scientific domains

Development of Flutter Constraints for High-fidelity Aerostructural Optimization

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143080/1/6.2017-4455.pd

Aerostructural design optimization of a 100-passenger regional jet with surrogate-based mission analysis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106481/1/AIAA2013-4372.pd