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Linear Algebra

Numerical linear algebra lies at the core of virtually all scientific computing. It provides the mathematical basis for operating on all geometric and image data, it is the foundation for the numerical solution of ordinary and partial differential equations, and it has become the central toolbox for the current hype-theme in computing: big data analytics.

The deep relationship between numerical linear algebra and differential as well as integral equations remains important to engineering and science. Unless explicit methods are being used, the discretization of PDEs leads to systems of linear or nonlinear equations. The nonlinear case requires the repeated solution of linear equations. For most equations and discretization methods, the linear matrix systems are sparse. CERFACS has thirty years of expertise in solving such systems and is internationally acknowledged as one of the leading research centres in this field. During the last decade, work has centred on developing direct methods with a high degree of parallelism. More recently, the focus at Cerfacs lies on highly-parallel iterative solvers and on using these in hybrid methods to extend the capability of direct methods. Furthermore, the Algo team concentrates on multigrid and multilevel methods which are among the primary candidates to achieve the scalability and performance needed for future extreme scale computing. To show the applicability to real-world engineering problems we have been testing a range of all these solution methods for large scale problems in collaboration with our academic and industrial partners.


Some examples of our recent research work:

Sparse direct methods, hybrid direct-iterative and iterative methods

We focus on core problems in numerical linear algebra that are relevant for both CERFACS, its shareholders and are of academic interest. For example, we worked on solution methods for linear systems arising in the structural analysis of a reactor containment building with our industrial partner EDF. The developed iterative solver showed excellent convergence in only a few iterations for this problem [2]. It has been made available to EDF's finite-element code code_aster through the implementation in the open source linear algebra library PETSc. An example of our academic research work is the recently finished PhD thesis of Philippe Leleux on Hybrid direct and iterative solvers for sparse indefinite and overdetermined systems on future exascale architectures, in which attention is given to iterative and hybrid methods.



Multilevel and multigrid methods

Multigrid methods belong to the few solvers that have scalable numerical complexity and are thus among the primary candidates to exploit future extreme scale computing to its full potential. A current research topic is to develop such hierarchical algorithms and the software techniques to implement them on massively parallel and heterogeneous computer systems. The algo team takes part in the H2020 Energy oriented Centre of Excellence EoCoE 2. Here, a tailored multigrid solver for the gyrokinetic Poisson equation on disk-like geometries described by curvilinear coordinates has been developed [1]. This algorithm has the potential for highly parallel scalability and, since it is a matrix free algorithm, it has a low memory footprint.


[1] Kuehn, M., Kruse, C., Ruede, U., Energy-minimizing, symmetric finite differences for anisotropic meshes and energy functional extrapolation, 2020, https://hal.archives-ouvertes.fr/hal-02941899/document

[2] Kruse, C., Darrigrand, V., Tardieu, N. et al. Application of an iterative Golub-Kahan algorithm to structural mechanics problems with multi-point constraints. Adv. Model. and Simul. in Eng. Sci. 7, 45 (2020). https://doi.org/10.1186/s40323-020-00181-2


Catherine Lambert awarded Officer in the national order of Merit

Brigitte Yzel |  31 May 2022

Catherine LAMBERT, President of Cerfacs, has been promoted to the grade of officer in the national order of Merit, on the proposal of Mrs. Frédérique Vidal, Minister of Higher Education, Research and Innovation. Antoine PETIT, President and CEO of the CNRS, presented the insignia to Catherine LAMBERT during a ceremony that brought together many actors from the space, aeronautics, environment and digital sectors. Antoine PETIT: "Catherine's interpersonal skills, her ability to step back and understand very different environments (research, industry, politics) in order to develop a collective vision are the hallmarks of her career. Catherine is one of those people with whom you naturally feel confident, with whom you want to build something that goes beyond all of us to go further. With this honor, the Cerfacs teams are also rewarded.Read more

Sparse Days in Saint-Girons IV

Brigitte Yzel |  29 March 2022

Sparse Days Meeting 2022 🗓️  20-22 June 2022  @ Saint-Girons, France   🌐   Sparse Days 2022 will be held in Saint-Girons, Ariège, from 20-22 June. This enhanced version of Sparse Days is being co-organized by Cerfacs and ENSEEIHT/IRIT. It will be the fourth meeting in Saint- Girons following the tradition of the previous meetings held in 1994, 2003, and 2015. The tradition involves coupling our highly successful annual technical meeting with the ambience and hospitality of this wonderful Pyrenean town which encourages fruitful informal exchanges between participants.    Read more