Short bio

I prepared my Ph.D. at Inria-Paris and Sorbonne University (Paris — VI). It was funded by TOTAL S.A. From January 2019 to July 2020 I was a Max Planck Society postdoctoral research fellow in the NLMA team in the CSC group. Starting from August 2020, I hold a research position at the Computational Mathematics Group, STFC, UKRI.


Research items

  • High performance computing

  • Numerical linear algebra

  • Tensor methods

  • Krylov subspace methods

  • Domain decomposition methods


  • H. Al Daas, T. Rees, J. Scott.

Two-level Nyström--Schur preconditioner for sparse symmetric positive definite matrices. 2021.


  • H. Al Daas, G. Ballard, P. Benner.

Parallel Algorithms for Tensor Train Arithmetic. 2020.


  • P. Goyal, H. Al Daas, P. Benner.

Low-Rank and Total Variation Regularization and Its Application to Image Recovery. 2020.



  • H. Al Daas, L. Grigori, P. Jolivet, P. H. Tournier.

A Multilevel Schwarz Preconditioner Based on a Hierarchy of Robust Coarse Spaces. 2021.

Accepted in SIAM Journal for Scientific Computing, in press. PDF, bibtex.

Code for reproducing the results available here, PETSc interface through the HPDDM package, PCHPDDM.

  • H. Al Daas, L. Grigori, P. Henon, P. Ricoux.

Recycling Krylov Subspaces and Truncating Deflation Subspaces for Solving Sequence of Linear Systems. 2020

Accepted in ACM Transactions on Mathematical Software. PDF, bibtex.

  • H. Al Daas.

Solving linear systems arising from reservoirs modeling. Ph.D. thesis, PDF, bibtex.

  • H. Al Daas, L. Grigori.

A Class of Efficient Locally Constructed Preconditioners Based on Coarse Spaces. 2019.

SIAM Journal on Matrix Analysis and Applications. PDF.

  • H. Al Daas, L. Grigori, P. Hénon, Ph. Ricoux.

Enlarged GMRES for solving linear systems with one or multiple right-hand sides. 2018.

IMA Journal. PDF.

Selected talks

  • Communication-avoiding orthogonalization algorithm for tensor trains, GAMM ANLA 2019, Chemnitz, Germany

  • Efficient algebraic coarse spaces, Sparse Days 2018, Toulouse, France

  • Deflation subspaces and GMRES for solving a sequence of linear systems, PMAA18, Zurich, Switzerland

  • Enlarged GMRES for reducing communication, SIAM PP18, MS 28, Tokyo, Japan

  • Krylov subspace methods and deflation strategies, Junior Seminar at INRIA- Paris, France

  • Enlarged GMRES for a sequence of linear systems, MATHIAS18, Paris, France

  • Enlarged GMRES, SIAM CSE17, MS254, Atlanta, USA

  • GMRES based on enlarged Krylov subspaces, SIAM PP16, MS12, Paris, France

Research stays

  • CSTJF, centre scientifique TOTAL, Pau, collaboration with Pascal Hénon (Jan.-Feb. 2018)

  • CEMRACS, CIRM, Marseille, 6-week summer school (Jul.-Aug. 2016)

  • University of California, Berkeley, BeBOP group. Five-month visit in James Demmel’s research group (Jan.-May 2016)


  • Journal(s)

  • Conference(s)

    • PASC

    • EuroPar


  • Co-developer

    • CPaLAMeM: C Parallel Linear Algebra Memory Management in PreAlps package (several linear solvers and preconditioners)

  • Developer

    • cTT, pcTT: C and C-MPI implementation of TT tensor arithmetic operations

    • EGMRES, GMRES-MDR and Block GMRES-MDR: C-MPI implementation of enlarged GMRES with deflated restarting, GMRES with Modified Deflated Restart, and Block GMRES-MDR with different variants of deflation strategies


  • 2019 Numerical Linear Algebra, Bachelor level. Teaching Assistant, Otto von Guericke University, Magdeburg, Germany

  • 2017 Calculus, Introduction to Analysis for first year students. Teaching Assistant, UPMC, Paris, France

  • 2015 Numerical analysis, Scientific computation for third year students. Teaching Assistant, ENSAE, Paris, France