arXiv subjects

Zbigniew Piotrowski

Publications and source records attributed to Zbigniew Piotrowski.

4 recordsLinked to original sources

arXiv2026

What Limits Robustness in Deep Image Watermarking: An Analysis of Mechanisms and Their Scaling Across Capacities

Robustness remains the principal open problem in deep image watermarking, and what limits it becomes sharper as payload grows. This paper asks whether capacity is itself the limit or only makes other limits visible, and answers in two parts. The first organizes the distortions a watermark must survive and the strategies developed to resist them, ordering each by the axis that governs it: payload capacity for the distortions, differentiability for the strategies. The second identifies and measures three mechanisms that limit robustness in schemes mapping the payload onto a spatial block grid with extraction trained separately from a frozen embedder: desynchronization of the payload grid, the resistance of codec-induced distortion to training, and the narrowing of the usable embedding-strength window. Payloads from 64 to 16384 bits are measured, well beyond the range those strategies address. Training the extraction stage against a codec proves not merely ineffective but harmful, degrading the reading at the operating points used in training. The limits follow the class of distortion rather than capacity itself, and none is removed by further training on the extraction side, because all three arise before extraction. An evaluation protocol making claims of generalization verifiable is also contributed. The conclusions are properties of a class of designs rather than of one implementation.

cs.CR↗

arXiv2019

Report on energy-efficiency evaluation of several NWP model configurations

This document is one of the deliverable reports created for the ESCAPE project. ESCAPE stands for Energy-efficient Scalable Algorithms for Weather Prediction at Exascale. The project develops world-class, extreme-scale computing capabilities for European operational numerical weather prediction and future climate models. This is done by identifying Weather & Climate dwarfs which are key patterns in terms of computation and communication (in the spirit of the Berkeley dwarfs). These dwarfs are then optimised for different hardware architectures (single and multi-node) and alternative algorithms are explored. Performance portability is addressed through the use of domain specific languages. In this deliverable we report on energy consumption measurements of a number of NWP models/dwarfs on the Intel E5-2697v4 processor. The chosen energy metrics and energy measurement methods are documented. Energy measurements are performed on the Bi-Fourier dwarf (BiFFT), the Acraneb dwarf, the ALARO 2.5 km Local Area Model reference configuration (Bénard et al. 2010, Bubnova et al. 1995) and on the COSMO-EULAG Local Area Model reference configuration (Piotrowski et al. 2018). The results show a U-shaped dependence of the consumed energy on the wall-clock time performance. This shape can be explained from the dependence of the average power of the compute nodes on the total number of cores used. We compare the energy consumption of the BiFFT dwarf on the E5-2697v4 processor to that on the Optalysys optical processors. The latter are found to be much less energy costly, but at the same time it is also the only metric where they outperform the classical CPU. They are non-competitive as far as wall-clock time and especially numerical precision are concerned.

cs.DC↗

arXiv2019

Batch 2: Definition of novel Weather & Climate Dwarfs

This document is one of the deliverable reports created for the ESCAPE project. ESCAPE stands for Energy-efficient Scalable Algorithms for Weather Prediction at Exascale. The project develops world-class, extreme-scale computing capabilities for European operational numerical weather prediction and future climate models. This is done by identifying weather & climate dwarfs which are key patterns in terms of computation and communication (in the spirit of the Berkeley dwarfs). These dwarfs are then optimised for different hardware architectures (single and multi-node) and alternative algorithms are explored. Performance portability is addressed through the use of domain specific languages. This deliverable contains the description of the characteristics of a second set of so-called numerical weather & climate prediction dwarfs that form key functional components of prediction models in terms of the science that they encapsulate and in terms of computational cost they impose on the forecast production. The ESCAPE work flow between work packages centres on these dwarfs and hence their selection, their performance assessment, code adaptation and optimisation is crucial for the success of the project. These new dwarfs have been chosen with the purpose of extending the range of computational characteristic represented by the dwarfs previously selected in batch 1 (see Deliverable D1.1). The dwarfs have been made, their documentation has been compiled and the software has been made available on the software exchange platform. The dwarfs in this deliverable include a multigrid elliptic solver, a novel advection scheme for unstructured meshes, an advection scheme for structured meshes and a radiation scheme. This deliverable includes their scientific description and the guidance for installation, execution and testing.

cs.DC↗

arXiv2012

Baire and weakly Namioka spaces

Recall that a Hausdorff space $X$ is said to be Namioka if for every compact (Hausdorff) space $Y$ and every metric space $Z$, every separately continuous function $f:X\times{Y}\rightarrow{Z}$ is continuous on $D\times{Y}$ for some dense $G_δ$ subset $D$ of $X$. It is well known that in the class of all metrizable spaces, Namioka and Baire spaces coincide (Saint-Raymond, 1983). Further it is known that every completely regular Namioka space is Baire and that every separable Baire space is Namioka (Saint-Raymond, 1983). In our paper we study spaces $X$, we call them weakly Namioka, for which the conclusion of the theorem for Namioka spaces holds provided that the assumption of compactness of $Y$ is replaced by second countability of $Y$. We will prove that in the class of all completely regular separable spaces and in the class of all perfectly normal spaces, $X$ is Baire if and only if it is weakly Namioka.

math.GN↗