Computing Invariants with Transformers: Experimental Scalability and Accuracy

International audienceUsing abstract interpretation, invariants are usually obtained by solving iteratively a system of equations linking preconditions according to program statements. However, it is also possible to abstract first the statements as transformers, and then propagate the preconditions using the transformers. The second approach is modular because procedures and loops can be abstracted once and for all, avoiding an iterative resolution over the call graph and all the control flow graphs. However, the transformer approach based on polyhedral abstract domains encurs two penalties: some invariant accuracy may be lost when computing transformers, and the execution time may increase exponentially because the dimension of a transformer is twice the dimension of a precondition. The purposes of this article are 1) to measure the benefits of the modular approach and its drawbacks in terms of execution time and accuracy using significant examples and a newly developed benchmark for loop invariant analysis, ALICe, 2) to present a new technique designed to reduce the accuracy loss when computing transformers, 3) to evaluate experimentally the accuracy gains this new technique and other previously discussed ones provide with ALICe test cases and 4) to compare the executions times and accuracies of different tools, ASPIC, ISL, PAGAI and PIPS. Our results suggest that the transformer-based approach used in PIPS, once improved with transformer lists, is as accurate as the other tools when dealing with the ALICe benchmark. Its modularity nevertheless leads to shorter execution times when dealing with nested loops and procedure calls found in real applications

Preservation of Lyapunov-Theoretic Proofs: From Real to Floating-Point Arithmetic

In a paper, Feron presents how Lyapunov-theoretic proofs of stability can be migrated toward computer-readable and verifiable certificates of control software behavior by relying of Floyd's and Hoare's proof system. However, Lyapunov-theoretic proofs are addressed towards exact, real arithmetic and do not accurately represent the behavior of realistic programs run with machine arithmetic. We address the issue of preserving those proofs in presence of rounding errors resulting from the use of floating-point arithmetic: we present an automatic tool, based on a theoretical framework the soundness of which is proved in Coq, that translates Feron's proof invariants on real arithmetic to similar invariants on floating-point numbers, and preserves the proof structure. We show how our methodology allows to verify whether stability invariants still hold for the concrete implementation of the controller. We study in details the application of our tool to the open-loop system of Feron's paper and show that stability is preserved out of the box. We also translate Feron's proof for the closed-loop system, and discuss the conditions under which the system remains stable

ALICe: A Framework to Improve Affine Loop Invariant Computation

International audienceA crucial point in program analysis is the computation of loop invariants. Accurate invariants are required to prove properties on a program but they are difficult to compute. Extensive research has been carried out but, to the best of our knowledge, no benchmark has ever been developed to compare algorithms and tools. We present ALICe, a toolset to compare automatic computation techniques of affine loop scalar invariants. It comes with a benchmark that we built using 102 test cases which we found in the loop invariant bibliography, and interfaces with three analysis programs, that rely on different techniques: Aspic, ISL and PIPS. Conversion tools are provided to handle format heterogeneity of these programs. Experimental results show the importance of model coding and the poor performances of PIPS on concurrent loops. To tackle these issues, we use two model restructurations techniques whose correctness is proved in Coq, and discuss the improvements realized

Characterization of juvenile pyroclasts from the Kos Plateau Tuff (Aegean Arc): insights into the eruptive dynamics of a large rhyolitic eruption

Silicic pumices formed during explosive volcanic eruptions are faithful recorders of the state of the magma in the conduit, close to or at the fragmentation level. We have characterized four types of pumices from the non-welded rhyolitic Kos Plateau Tuff, which erupted 161,000years ago in the East Aegean Arc, Greece. The dominant type of pumice (>90vol.%) shows highly elongated tubular vesicles. These tube pumices occur throughout the eruption. Less common pumice types include: (1) "frothy” pumice (highly porous with large, sub-rounded vesicles), which form 5-10vol.% of the coarsest pyroclastic flow deposits, (2) dominantly "microvesicular” and systematically crystal-poor pumices, which are found in early erupted, fine-grained pyroclastic flow units, and are characterized by many small (<50μm in diameter) vesicles and few mm-sized, irregular voids, (3) grey or banded pumices, indicating the interaction between the rhyolite and a more mafic magma, which are found throughout the eruption sequence and display highly irregular bubble shapes. Except for the grey-banded pumices, all three other types are compositionally identical and were generated synchronously as they are found in the same pyroclastic units. They, therefore, record different conditions in the volcanic conduit leading to variable bubble nucleation, growth and coalescence. A total of 74 pumice samples have been characterized using thin section observation, SEM imagery, porosimetry, and permeametry. We show that the four pumice types have distinct total and connected porosity, tortuosity and permeability. Grey-banded pumices show large variations in petrophysical characteristics as a response to mingling of two different magmas. The microvesicular, crystal-poor, pumices have a bimodal bubble size distribution, interpreted as reflecting an early heterogeneous bubble nucleation event followed by homogeneous bubble nucleation close to fragmentation. Finally, the significant differences in porosity, tortuosity and permeability in compositionally identical tube and frothy pumices are the result of variable shear rates in different parts of the conduit. Differential shear rates may be the result of either: (1) pure shear, inducing a vertical progression from frothy to tube and implying a relatively thick fragmentation zone to produce both types of pumices at the same time or (2) localized simple shear, inducing strongly tubular vesicles along the wall and near-spherical bubbles in the centre of the conduit and not necessarily requiring a thick fragmentation zon

Comportement thermomécanique d'un béton ordinaire en compression cyclée : expérience et modélisation

International audienceLes faibles phénomènes thermiques apparaissant lors d’essais de compression sur un bétonordinaire ont pu être observés par thermographie infrarouge. Pour leur modélisation etleur interprétation, il est proposé une extension thermomécanique du modèle élastiqueendommageable de M. Frémond et B. Nedjar. Elle permet un dialogue intéressant entreles résultats expérimentaux et ceux obtenus par simulation numérique.Infrared thermography observations permit to show thermal phenomena occurring on aplain concrete during a compressive test. A modelling of the thermomechanical behaviourof this materials is proposed as an extension of M. Frémond and B. Nedjar’s model. Itpermits an interesting dialog between the experimental results and those obtained bya numerical simulation of a simple compressive test

Mise en évidence et quantification des couplages thermomécaniques réversibles et irréversibles dans les bétons sains et endommagés par des cycles gel-dégel

International audienceShowing and measuring of reversible or not thermomechanical couplings in undamaged and freezing/thawing damaged concrete We study thermal phenomena which occur during compressive loading tests on some damaged or not concrete. Two calorific effects are shown through an experimental study using infrared thermography. The first, intrinsically reversible, is due to the thermoelastic coupling. The second is due to damage concrete state.À partir de l'observation fine par thermographie infrarouge des phénomènes thermiques mis en jeu lors de sollicitations de compression quasi-statiques, sont identifiées et quantifiées l'incidence de l'effet thermoélastique et celle de la dissipation intrinsèque associée à l'état d'endommagement d'un béton ayant subi des cycles gel-dégel

La lecture des œuvres complètes en contexte scolaire au Québec

Au Québec, les récentes réformes curriculaires témoignent d’exigences élevées quant au nombre d’œuvres complètes à lire en formation pré-universitaire, mais accordent une grande liberté aux enseignants pour la sélection des titres. Les auteurs se fondent sur les résultats d’une vaste enquête pour dresser un état des lieux des exigences des enseignants en matière de lecture des œuvres, des finalités associées à cette pratique et des corpus choisis. Les enseignants du primaire et du secondaire ciblent le développement du plaisir de lire, ceux du collégial visent la constitution d’une culture littéraire de base : la première est centrée sur la littérature québécoise alors que la seconde prend en compte le patrimoine français.In Quebec, the recent curricular reforms are very demanding in terms of the number of whole works to be read in pre-university training, but give teachers free rein for choosing which books. The authors draw from the findings of an extensive study to review teachers’ requirements in terms of reading works, the aims of this practice and the texts chosen. Primary and secondary school teachers want to develop a liking for reading while high school teachers focus on fostering a basic literary culture: the first is based on Quebecker literature while the second embraces French heritage.En Quebec, las recientes reformas curriculares atestiguan unas elevadas exigencias en cuanto al número de obras completas que deben leerse durante la formación preuniversitaria, pero les conceden una gran libertad a los docentes a la hora de elegir los títulos. Los autores se basan en los resultados de una amplia encuesta para establecer un estado de la cuestión de las exigencias de los docentes en lo que toca a la lectura de las obras, finalidades asociadas a esta práctica y corpus seleccionados. Los docentes de primaria y de secundaria se proponen desarrollar el placer de la lectura, y los de postsecundaria se esmeran por cimentar una cultura literaria básica: la primera se centra en la cultura quebequesa, mientras que la segunda tiene en cuenta el patrimonio francés

Mise en évidence par granularité en lumière blanche de phénomènes de multilocalisation de la déformation pour les bétons de poudres réactivessollicités en traction

International audienceShowing of multilocalisation strain phenomena occurring in reactive powders concrete during tensile tests by digital speckle images correlation in lighting white mode From kinematic observations by granularity in whiting light mode based on a technique of digital speckle images correlation, the behaviour in tension of a reactive powders concrete is studied. The measures show several localisation areas of the deformation fields and the role of the fibres in the transmission of the stresses in the neighbourhood of a damaged area.Le comportement en traction d'un béton de poudres réactives est étudié à partir d'obser-vations cinématiques par granularité en lumière blanche fondées sur une technique d'inter-corrélation d'images. Les mesures mettent en évidence pour des BPR suffisamment fibrés, à la différence des bétons ordinaires, l'apparition systématique de plusieurs zones de loca-lisation de la déformation et le rôle des fibres dans la redistribution des efforts au voisinage d'une zone fissurée

Minimally invasive versus open pancreatoduodenectomy for pancreatic and peri-ampullary neoplasm (DIPLOMA-2):study protocol for an international multicenter patient-blinded randomized controlled trial

Background: Minimally invasive pancreatoduodenectomy (MIPD) aims to reduce the negative impact of surgery as compared to open pancreatoduodenectomy (OPD) and is increasingly becoming part of clinical practice for selected patients worldwide. However, the safety of MIPD remains a topic of debate and the potential shorter time to functional recovery needs to be confirmed. To guide safe implementation of MIPD, large-scale international randomized trials comparing MIPD and OPD in experienced high-volume centers are needed. We hypothesize that MIPD is non-inferior in terms of overall complications, but superior regarding time to functional recovery, as compared to OPD. Methods/design: The DIPLOMA-2 trial is an international randomized controlled, patient-blinded, non-inferiority trial performed in 14 high-volume pancreatic centers in Europe with a minimum annual volume of 30 MIPD and 30 OPD. A total of 288 patients with an indication for elective pancreatoduodenectomy for pre-malignant and malignant disease, eligible for both open and minimally invasive approach, are randomly allocated for MIPD or OPD in a 2:1 ratio. Centers perform either laparoscopic or robot-assisted MIPD based on their surgical expertise. The primary outcome is the Comprehensive Complication Index (CCI®), measuring all complications graded according to the Clavien-Dindo classification up to 90 days after surgery. The sample size is calculated with the following assumptions: 2.5% one-sided significance level (α), 80% power (1-β), expected difference of the mean CCI® score of 0 points between MIPD and OPD, and a non-inferiority margin of 7.5 points. The main secondary outcome is time to functional recovery, which will be analyzed for superiority. Other secondary outcomes include post-operative 90-day Fitbit™ measured activity, operative outcomes (e.g., blood loss, operative time, conversion to open surgery, surgeon-reported outcomes), oncological findings in case of malignancy (e.g., R0-resection rate, time to adjuvant treatment, survival), postoperative outcomes (e.g., clinically relevant complications), healthcare resource utilization (length of stay, readmissions, intensive care stay), quality of life, and costs. Postoperative follow-up is up to 36 months. Discussion: The DIPLOMA-2 trial aims to establish the safety of MIPD as the new standard of care for this selected patient population undergoing pancreatoduodenectomy in high-volume centers, ultimately aiming for superior patient recovery. Trial registration: ISRCTN27483786. Registered on August 2, 2023.</p