Dune Developer Meeting 2020 in Heidelberg

Date and Location

The developer meeting is held on February 12-13, 2020 at IWR Room 1/414 in Heidelberg. We invite all DUNE developers and contributors to participate.

Tentative Schedule

Feb. 12 10:00 - 12:00  Meeting
12:00 - 13:00  Lunch
13:00 - 18:00  Meeting
Feb. 139:00 - 12:00Meeting
12:00 - 13:00  Lunch
13:00 - 18:00  Meeting


  • Peter Bastian
  • Markus Blatt
  • Andreas Dedner (only Wednesday afternoon)
  • Nils Dreier
  • Christian Engwer
  • Jorrit (Jö) Fahlke
  • Christoph Grüninger (only Wednesday, Feb 12)
  • René Heß
  • Lasse Hinrichsen
  • Dominic Kempf
  • Ole Klein
  • Robert Klöfkorn (only Wednesday afternoon)
  • Santiago Ospina de los Rios
  • Simon Praetorius
  • Oliver Sander
  • Linus Seelinger
  • Michal Toth

Proposed topics

Please use the edit function to add your topics or write an email to Markus.



  • Christoph: Vote on Simon becoming a Dune core developer

    • In favour: 6
    • Against: 0
    • Abstain: 0

    Welcome Simon!

  • Christian: I suggest that we decide on a code-of-conduct. This should ensure that Dune is received as an open welcoming community. See for example the one of PETSc.

    • Need particular proposal, need more information


  • Jö: What is the state of dune-gitlab?

    Is currently staying in HD, Peter thinks there will be people in ~0.5 year to take care of a general IWR gitlab.

    Until then, can we have more people with admin right for core? -> Rene can add people?

  • Jö: Seeking co-maintainers for mailing list servers (reduce bus factor) -> Markus


  • Christoph: Bump required compiler support from C++11 to C++14, i.e., GCC 4.9 to GCC 7 (from May 2017) and from ancient Clang 3.8 to Clang 5. Given Dune 2.8 will be released in 2021 or even later, this would enable us to use convenient C++ techniques and reduce the number of feature checks.

    • Actually, support C++17 to the extent that GCC7 supports.
    • Mingw: can live with GCC7
    • Clang? 7 is in Debian buster
      • Dumux using Clang 5
      • Ubuntu Bionic Clang6
    • Clusters not an issue anymore, usually have modules with newer compilers

    Conclusion: C++17 to the extent supported by GCC7 and Clang5

    • excludes replacement of class objects containing reference members (not supported in Clang5
    • Christoph will make a list of more excluded features
    • Who can update the CI system? Image building for CI system is broken currently. Simon will give it a try.
  • Christoph: Getting rid of dune-grid-howto. It’s in an embarrassing state. It could be replaced by Oliver’s book once this is published.

    Possible alternative: “Recipes” by Linus.

    Conclusion: dune-grid-howto won’t be part of the next release. Christoph will take care.

  • Christoph: I’d like to make a two-hour session to revise old merge request and issues. We should either decide what to do about them or close them. -> group work

  • Christoph: Reduce number of core modules, cf. mailing list thread

    • RK: I think the number of core modules is ok. E.g. dune-istl should definitively stay separate from dune-grid. The one module I would like to see merged is dune-python into the various core modules as discussed during the last meeting.
    • Christoph: I’d like to see dune-geometry and/or dune-istl merged to dune-common. Many aspects of istl and common are difficult to separate (defines of matrices, basic linear algebra). Dune-geometry is very specific / fine granular (geometry and quadrature rules) that it is not justified to be a module of its own. Including Python support sounds like a good idea.
    • Discussion:
      • higher-order geometries might require localfunctions, and localfunctions requires geometry
      • tooling to simplify releases?
      • is there a limit in the number of core modules?
      • merging or moving dune-uggrid? Remove splitting into dune-grid/dune-uggrid?
      • Make dune-functions a core module? (not voted now)
      • Decision:
        • dune-typetree -> dune-common (VOTE: yes) (need some cleanup)

        • Change of namespace in dune-typetree

          1. Dune:: (VOTES: 2)
          2. Dune::TypeTree (VOTES: 14)
          3. Dune::Common::TypeTree (VOTES: 10)
          4. Dune::Common (VOTES: 2)

          VOTE on 2: 11, VOTE on 3: 6, Decision: Dune::TypeTree

  • Markus: What ist the status of EXADUNE, what should we integrate back?

    • Status: simd interfaces, vectorization of istl solvers, block-krylov methods, multi-threaded/GPU supported solvers (difficult to integrate), block-structured grids, higher-order methods, pipelined/communication-hiding krylov methods
    • Integration: block-krylov methods (dune-istl), (partially) higher-order DG methods (dune-pdelab)
    • Discussion:
      • backward iteration over grid elements (interface change?)
      • multi-threaded istl solvers? (from kascade? from exadune? tbb-based?)
  • Linus: add a module.hh header in every module including everything from that module

    • RK: too many dependencies -> lead to recompile everything
    • don’t use this header in any other core module?
    • benefits? beginners have to look for the headers to include
    • cmake macro to generate header list?
    • are there incompatible headers?
  • Simon: We have to update docker images to clang5 & test with c++17

  • Simon: Is there a place to check of user dune projects?

    • OS: Modules page lack of structure (what is an extension?)
    • Proposal:
      • OS: Include more descriptions to the modules (OS do it)
      • Simon: Add more structure to the sections
        • Have a web for each tag with the modules including such tag
  • Linus: examples should compile and run in the CI

    • Very simple example witch is working and is documented in doxygen and that is also compiled and run in the CI
    • There are enough tools in Doxygen to fully document specific parts of the code (e.g. snippet, link pages, show partial part of a file)
    • See example: https://www.dune-project.org/doxygen/pdelab/master/group__pdelab__recipes.html
    • This avoids that examples get outdated and give users the idea of how to use the software
    • Use folder /doc/recepies/ so that is easy to link later in the webpage and add files to ´dune_test´
  • Linus: Is there interest for functionality to write tracing information in OTF-2 file-format?

    • It records information the taks it is performing (entring and leaving a section in the code) and with the format one can get visualization of the load balance with VTE (there are other possibilities)
    • With the OTF2 is a little bit complicated to instrument, so the proposal is to add a facility to trace easier code.
    • Linus will send a merge request with the feature
  • Simon: Several links in the webpage are broken.

Not yet discussed:

  • Jö: Cheat-sheet?
  • Rober & Andreas: let’s talk about 3.0?
    • Simon: Future plans?



  • Linus: Parallel communication using information about rank, some extension is needed in the data handles for the ParallelIndexSet

    • Nils and Robert are working on something already (although in a Private issue).
  • Closing issues:

    • GMSH reader:
      • Jo referes to indexing problems with gmsh (See https://gitlab.dune-project.org/flyspray/FS/issues/1698)
      • Simon: There is some work done to the gmsh format 4.0 (Parametrized geometry)
      • GMSH 4 is not compatible with gmsh 2 format reader. Parallel information is the main change from it.
      • The reader complains when it finds PhisicalEntities.
        • Christian Use component readers for each section.
    • The class VirtualFunction that fulfills the same purpose as std::function. We agree to deprecate it.
    • viewThread proposal for the grid -> closed.

    • Christian: Can we get rid of FORTRAN? It is needed for LAPACK.
    • Eigen & PETSc uses a LAPACK without fortran so we know it’s possible.

Logging library:

  • Dominic: Discuss inclusion of (support for) a logging library
  • Christian: I’m in favour of an external solution. We have to keep our maintenance effort in mind.
  • Need for better logging support?
  • Include libfmt (or something similar)?
  • Needs more information! Comparison of logging libraries, more arguments for dune-logging, maintainability of dune-logging? hard or soft dependency? hierarchical logging? interface changes necessary to use loggers in dune classes?


  • OS: The makers of CurvilinearGrid have relicensed their code, and the license is now dune-compatible. Can we import their implementation of a curvilinear geometry(!) into dune-geometry?
    • Simon worked some with it
    • They have a different numbering of langrange base nodes
    • Simon is working on a extended geometry


  • OS: ALUGrid implements an extended GridFactory that allows for distributed grid setup. Can we make that an official interface?
    • RK: Sounds like a good idea.
    • Christoph: +1
    • Here the interface changes we are talking about:
/** \brief insert a vertex into the coarse grid including the vertex's globally unique id
     *  \param[in]  pos       position of the vertex
     *  \param[in]  globalId  globally unique id for vertex (e.g. globally unique vertex index)
    void insertVertex ( const VertexInputType &pos, const VertexId globalId );

    // for ALUGrid it is also beneficial to have but this is not mandatory
    virtual void
    insertProcessBorder ( const std::vector< VertexId >& vertices );
- Additional information about rank sharing the vertices?
- Decision:
    - Andreas: Submit proposal on GitLab to see the details
  • OS: Interface clarification: when the grid changes, do GridView objects remain valid? What about IdSets?
    • Example: YaspGrid: gridview is invalid after grid changes
    • Documentation!
    • Carsten: See decision in dev-meeting 2009


  • Simon: Langrange functions have unclear semantics, different implementations using inconsistent ordering of Lagrange nodes. Ordering should be documented.
  • Simon: Factory and cache have very different interfaces, you can’t easily switch from one to the other.


  • Nils: Parallel SolverFactory
    • Polymorphic communication object
    • User interface
  • OS: I keep hearing from people that the RemoteIndex implementation is showing its age. Can we organize a redesign/rewrite?
    • Christian: The ParallelIndexSets are an aimplementation and not an interface. Nils and RK are currently working on a proposal for an interface, for which the ParallelIndexSets can be a particular implementation. My goal would be to have a coarse grained dynamic interface (in ISTL), which can then be fed with data from a ParallelIndexSet or from a Grid or something else…


  • Simon: Parallelization of dune-functions bases. Missing tools and utilities, e.g.
    • Iteration over all DOFs on entities
    • (global) IDs of DOFs
    • Introduction of PartitionSet in several algorithms
    • Something like Twist-Uitlities for uniquely identifying the order of DOFs on sub entities (also global unique)
    • ParallelIndexSet for MultiIndices
    • Maybe something like dune-grid:GlobalIndexSet but for the DOFs
    • Properly wrapped local bases for DG discretization (association of local DOFs to the element and not to the sub-entities)
  • OS: New ideas on how to support non-affine families of finite elements?


  • Module: https://github.com/spraetor/dune-vtk
  • OS: Simon has a module for reading and writing VTK stuff doing much more than the stuff integrated in dune-grid, including higher order functions and structured grid.
  • This module can write specific vtk formats that are more compact. Paraview is much faster when using these formats.
    • Subsampling is still not implemented.
    • Can write quadratic data (Not so easy to visualize in paraview)
    • Structured and rectangular grids.
    • PolyData not implemented (1D is in dune-grid because it was the only way possible to write 1D data)
  • Christian: How does it compress data?
    • Is stored in binary blocks compressed: collect - compress - write - come back and set the position of the data.
  • Why don’t we use the VTK library?
    • Is not very easy to use. Huge library. No smooth transitions between versions.
  • Reader:
    • Data collector: get grid info and its data, then decide whether to write continuous or discontinuous data. It is very flexible to be combined with other data collectors.
    • Parallel grid format:
      • If grid factory does have the global ID interface then it builds the grid on each processor
      • otherwise it gets serialized in one processor and then load balance.
  • Know Bug: When YaspGrid has periodic boundaries, it simply produces wrong results.
  • In the long run the idea is to complete the missing features and to merge it into dune-grid.

Discretization modules (FEM, PDELab, …)

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