Dear all, Mark Adams, the developer of the PETSc algebraic multigrid solver GAMG is giving two talks tomorrow afternoon, one an introduction to multigrid methods, the second about segmental refinement. See details below. Lawrence

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From: Ben Yeager <b.yeager14@imperial.ac.uk> Subject: [AMCG-Seminars] AMCG seminars this Thursday - multigrid methods and segmental refinement Date: 30 June 2015 09:19:36 BST To: "amcg-seminars@imperial.ac.uk" <amcg-seminars@imperial.ac.uk>

Hello all,

We have two special edition Seminars on multi grids methods this Thursday, 3pm-4pm and 4pm-5pm in the Grantham boardroom, by Mark Adams (http://crd.lbl.gov/departments/applied-mathematics/scalable-solvers-group/me... <http://crd.lbl.gov/departments/applied-mathematics/scalable-solvers-group/members/staff-members/mark-adams/>) who has previously won the Gordon Bell Award in SuperComputing with his multigrid software.

The first, from 15:00-16:00, will be an introduction to multigrid methods [see abstract below]. This should serve as excellent primer for anyone who is not already an expert on multi-grid methods.

The second seminar, from 16:10-17:00, will be a talk on segmental refinement - a multigrid technique for data locality, which focuses on algorithmic advances to improve the scalability of multigrid methods [see abstract below].

You are welcome to attend one or both of these talks

See below for more details.

Cheers, AMCG Seminars organisers

3pm - 4pm: Introduction to multigrid methods and primer for advanced methods: segmental refinement. I will give an overview of multigrid algorithms for the Laplacian, which are classic results from the 1970's, but are not widely understood in my experience. We cover some analysis using local Fourier analysis and sketch the proof for the asymptotic exactness of the non-iterative form of multigrid: full multigrid (FMG). An understanding of FMG is critical in the discussion of advanced methods like segmental refinement. We derive the non-linear form of multigrid: full approximation scheme (storage) FAS, and briefly introduce algebraic multigrid.

4:00pm-4:10pm: Short break

4:10pm-5pm: Segmental Refinement: A Multigrid Technique for Data Locality We investigate a domain decomposed multigrid technique, segmental refinement, for solving general nonlinear elliptic boundary value problems. Brandt and Diskin first proposed this method in 1994; we continue this work by analytically and experimentally investigating the complexity of the method. We confirm that interprocess communication can be eliminated on fine grids with modest amounts of extra work and storage, although we observe a dependence on an additional parameter not considered in the original analysis. We present a communication complexity analysis with a three-level memory model and report preliminary performance results with up to 64K cores of a Cray XC30. _______________________________________________ AMCG and Friends Seminar Series Mailing List AMCG-Seminars@imperial.ac.uk Subscription Options: https://mailman.ic.ac.uk/mailman/listinfo/amcg-seminars Webpage: http://amcg.ese.ic.ac.uk/index.php?title=Seminar_Series