Frequently Asked Questions about FeenoX
Jeremy Theler
2025-09-01

- 1 What is FeenoX?
- 2 How should I cite FeenoX?
- 3 What does FeenoX mean?
- 4 How should FeenoX be pronounced?
- 5 Why nothing happens when I double click on feenox.exe?
- 6 How do I create input decks for FeenoX?
- 7 Does FeenoX support beam and/or shell elements?
- 8 What license does FeenoX have?
- 9 Why is FeenoX written in C and not in…
  - 9.1 C++?
  - 9.2 Fortran?
  - 9.3 Python or R?
  - 9.4 Go, Rust or Julia?

  [1 What is FeenoX?]: #what-is-feenox
  [2 How should I cite FeenoX?]: #how-should-i-cite-feenox
  [3 What does FeenoX mean?]: #what-does-feenox-mean
  [4 How should FeenoX be pronounced?]: #how-should-feenox-be-pronounced
  [5 Why nothing happens when I double click on feenox.exe?]: #why-nothing-happens-when-i-double-click-on-feenox.exe
  [6 How do I create input decks for FeenoX?]: #how-do-i-create-input-decks-for-feenox
  [7 Does FeenoX support beam and/or shell elements?]: #does-feenox-support-beam-andor-shell-elements
  [8 What license does FeenoX have?]: #what-license-does-feenox-have
  [9 Why is FeenoX written in C and not in…]: #why-is-feenox-written-in-c-and-not-in
  [9.1 C++?]: #c
  [9.2 Fortran?]: #fortran
  [9.3 Python or R?]: #python-or-r
  [9.4 Go, Rust or Julia?]: #go-rust-or-julia

What is FeenoX?

It is “cloud-first a free no-fee no-X uniX-like finite-element(ish)
computational engineering tool.” Essentially, a finite-element program
with a particular design basis:

  FeenoX is to finite-element programs and libraries what Markdown is to
  word processors (like Word) and typesetting systems (like TeX),
  respectively.

In increasing order of complexity and comprehensiveness, these resources
explain what FeenoX is:

- The examples will give a brief overview of what FeenoX can do.

- The tutorials will walk your through how to use FeenoX to solve
  problems.

- The README in the GitHub repository has a brief introduction (after
  explaining why).

- Theler, J. (2024). FeenoX: a cloud-first finite-element(ish)
  computational engineering tool. Journal of Open Source Software,
  9(95), 5846. https://doi.org/10.21105/joss.05846

  [DOI]

- There is also a description in the documentation.

- FeenoX is an “offer” to a fictitious “tender” for a computational
  tool. The RFQ is the Software Requirements Specification and the
  explanation of how FeenoX addresses each requirement is the Software
  Design Specification.

- This presentation from August 2021 explains the SRS/SDS pair. The
  sources and the examples can be found in this Github repository. There
  is a recording of the presentation (audio is in Spanish).

- Finally the manual will be the ultimate guide.

  [FeenoX]: https://www.seamplex.com/feenox
  [examples]: https://www.seamplex.com/feenox/examples
  [tutorials]: https://www.seamplex.com/feenox/doc/tutorials
  [README]: https://www.seamplex.com/feenox/
  [GitHub repository]: https://github.com/seamplex/feenox/
  [DOI]: https://joss.theoj.org/papers/10.21105/joss.05846/status.svg
  [1]: https://doi.org/10.21105/joss.05846
  [description]: https://www.seamplex.com/feenox/doc/feenox-desc.html
  [documentation]: https://seamplex.com/feenox/doc/
  [Software Requirements Specification]: https://www.seamplex.com/feenox/doc/srs.pdf
  [presentation from August 2021]: (https://www.seamplex.com/feenox/doc/2021-feenox.pdf)
  [this Github repository]: https://github.com/gtheler/2021-presentation
  [recording of the presentation]: (https://youtu.be/-RJ5qn7E9uE)
  [manual]: https://www.seamplex.com/feenox/doc/feenox-manual.pdf

How should I cite FeenoX?

If you use FeenoX and need to cite it, use this BiBTeX entry that points
to the 2024 paper in JOSS:

    @article{feenox-2024,
    author = {Theler, Jeremy},
    doi = {10.21105/joss.05846},
    journal = {Journal of Open Source Software},
    month = mar,
    number = {95},
    pages = {5846},
    title = {{FeenoX: a cloud-first finite-element(ish) computational engineering tool}},
    url = {https://joss.theoj.org/papers/10.21105/joss.05846},
    volume = {9},
    year = {2024}
    }

If you are not using BiBTeX (which you should), just use the plain-text
APA format:

Theler, J. (2024). FeenoX: a cloud-first finite-element(ish)
computational engineering tool. Journal of Open Source Software, 9(95),
5846. https://doi.org/10.21105/joss.05846

  [BiBTeX]: https://www.bibtex.org/
  [the 2024 paper in JOSS]: https://joss.theoj.org/papers/10.21105/joss.05846

What does FeenoX mean?

It does not mean anything particular, but

- The last X makes it rhyme with Unix and Linux.
- “noX” means that there is no graphical (i.e. X) interface
- Fee-no means that there are no fees involved (free as in “free beer”)
- FeenoX is the successor of the now-superseded FEA program Fino
- It rhymes with FEniCS
- With some luck one can read “Finite ElEments NO-X”
- With mode luck, “FrEE” (as in “free speech”)

How should FeenoX be pronounced?

It would be something like fee-naaks: /fiːnɒks/
But whatever works for you is fine.

Why nothing happens when I double click on feenox.exe?

Because by design, FeenoX does not have a Graphical User Interface.
Instead, it works like a transfer function between one or more input
files and zero or more output files:

                                 +------------+
     mesh (*.msh)  }             |            |             { terminal
     data (*.dat)  } input ----> |   FeenoX   |----> output { data files
     input (*.fee) }             |            |             { post (vtk/msh)
                                 +------------+

Recall that FeenoX is designed as a cloud-first tool, and “the cloud”
runs on Unix (essentially GNU/Linux) so FeenoX is based on the Unix
philosophy. In this world, programs act like filters (i.e. transfer
functions). They are executed from a command-line terminal. So instead
of “double clicking” the executable, one has to open a terminal and
execute it there. Without any arguments it says how to use it:

    > feenox.exe
    FeenoX v0.2.14-gbbf48c9
    a free no-fee no-X uniX-like finite-element(ish) computational engineering tool

    usage: feenox [options] inputfile [replacement arguments] [petsc options]

      -h, --help         display options and detailed explanations of command-line usage
      -v, --version      display brief version information and exit
      -V, --versions     display detailed version information

    Run with --help for further explanations.
    >

With -h it gives more information:

    > feenox.exe -h
    usage: feenox [options] inputfile [replacement arguments] [petsc options]

      -h, --help         display options and detailed explanations of command-line usage
      -v, --version      display brief version information and exit
      -V, --versions     display detailed version information

      --progress         print ASCII progress bars when solving PDEs
      --mumps            ask PETSc to use the direct linear solver MUMPS
      --linear           force FeenoX to solve the PDE problem as linear
      --non-linear       force FeenoX to solve the PDE problem as non-linear

    Instructions will be read from standard input if “-” is passed as
    inputfile, i.e.

        $ echo 'PRINT 2+2' | feenox -
        4

    The optional [replacement arguments] part of the command line mean that
    each argument after the input file that does not start with an hyphen
    will be expanded verbatim in the input file in each occurrence of $1,
    $2, etc. For example

        $ echo 'PRINT $1+$2' | feenox - 3 4
        7

    PETSc and SLEPc options can be passed in [petsc options] as well, with
    the difference that two hyphens have to be used instead of only once.
    For example, to pass the PETSc option -ksp_view the actual FeenoX
    invocation should be

        $ feenox input.fee --ksp_view

    See https://www.seamplex.com/feenox/examples for annotated examples.

    Report bugs at https://github.com/seamplex/feenox/issues
    Ask questions at https://github.com/seamplex/feenox/discussions
    Feenox home page: https://www.seamplex.com/feenox/
    >

It is explained there that the main input file has to be given as the
first argument. So go to the tests or examples directory, find a test
you like and run it:

    > cd tests
    > feenox parallelepiped.fee
    0.000295443
    >

In any case, recall once again that FeenoX is a cloud-first tool, and
Windows is not cloud-friendly, let alone cloud-first. It is time to
re-think what you expect from a finite-element(ish) tool. If you still
need a GUI, please check CAEplex.

Try to avoid Windows as much as you can. The binaries are provided as
transitional packages for people that for some reason still use such an
outdated, anachronous, awful and invasive operating system. They are
compiled with Cygwin and have no support whatsoever. Really, really, get
rid of Windows ASAP.

  “It is really worth any amount of time and effort to get away from
  Windows if you are doing computational science.”

  https://lists.mcs.anl.gov/pipermail/petsc-users/2015-July/026388.html

  [Unix philosophy]: ./unix.md
  [CAEplex]: https://www.caeplex.com
  [Cygwin]: http://cygwin.com/

How do I create input decks for FeenoX?

FeenoX does not have “input decks.” It has “input files,” which are
syntactically-sugared English-like plain-text ASCII files that describe
the problem to be solved. First see the examples and the test directory.
Then read the documentation.

There are syntax highlighting files for Kate and for Vim that helps the
edition of input files. Contributions for other editors (emacs?) are
welcome.

[The Kate Text Editor can be used to prepare input files with syntax
highlighting.]

  [2]: https://www.seamplex.com/feenox/examples/
  [test directory]: https://github.com/seamplex/feenox/tree/main/tests
  [3]: https://www.seamplex.com/feenox/doc/
  [for Kate]: https://github.com/seamplex/feenox/blob/main/doc/feenox.xml
  [for Vim]: https://github.com/seamplex/feenox/blob/main/doc/fee.vim
  [The Kate Text Editor can be used to prepare input files with syntax highlighting.]:
    nafems-le10-problem-input.svg

Does FeenoX support beam and/or shell elements?

No, it currently supports solid elements only. Therefore,
three-dimensional problems need to have tetrahedra, hexahedra, prisms
and/or pyramids; and two-dimensional problems need to have triangles or
quadrangles.

It might support non-solid elements for elasticity in future versions,
though. Contributions are welcome. Check out the contributing
guidelines.

  [contributing guidelines]: https://www.seamplex.com/feenox/doc/#contributing-guidelines

What license does FeenoX have?

TL;DR:

- The code is GPLv3+: you can use it, modify it and re-distribute it
  freely (as in free speech) as long as you keep the same licensing
  terms.
- The documentation is released under the terms of the Creative Commons
  Attribution-ShareAlike 4.0 International License (CC BY-SA 4.0)

FeenoX is licensed under the terms of the GNU General Public License
version 3 or, at the user convenience, any later version. This means
that users get the four essential freedoms:[1]

0.  The freedom to run the program as they wish, for any purpose.
1.  The freedom to study how the program works, and change it so it does
    their computing as they wish.
2.  The freedom to redistribute copies so they can help others.
3.  The freedom to distribute copies of their modified versions to
    others.

So a free program has to be open source, but it also has to explicitly
provide the four freedoms above both through the written license and
through appropriate mechanisms to get, modify, compile, run and document
these modifications using well-established and/or reasonable
straightforward procedures. That is why licensing FeenoX as GPLv3+ also
implies that the source code and all the scripts and makefiles needed to
compile and run it are available for anyone that requires it (i.e. it is
compiled with ./configure && make). Anyone wanting to modify the program
either to fix bugs, improve it or add new features is free to do so. And
if they do not know how to program, the have the freedom to hire a
programmer to do it without needing to ask permission to the original
authors. Even more, the documentation is released under the terms of the
Creative Commons Attribution-ShareAlike 4.0 International License so
these new (or modified) features can be properly documented as well.

Nevertheless, since these original authors are the copyright holders,
they still can use it to either enforce or prevent further actions from
the users that receive FeenoX under the GPLv3+. In particular, the
license allows re-distribution of modified versions only if

a.  they are clearly marked as different from the original, and
b.  they are distributed under the same terms of the GPLv3+.

There are also some other subtle technicalities that need not be
discussed here such as

- what constitutes a modified version (which cannot be redistributed
  under a different license)
- what is an aggregate (in which each part be distributed under
  different licenses)
- usage over a network and the possibility of using AGPL instead of GPL
  to further enforce freedom

These issues are already taken into account in the FeenoX licensing
scheme.

It should be noted that not only is FeenoX free and open source, but
also all of the libraries it depends on (and their dependencies) also
are. It can also be compiled using free and open source build tool
chains running over free and open source operating systems.

[1]  There are some examples of pieces of computational software which
are described as “open source” in which even the first of the four
freedoms is denied. The most iconic case is that of Android, whose
sources are readily available online but there is no straightforward way
of updating one’s mobile phone firmware with a customized version, not
to mention vendor and hardware lock ins and the possibility of bricking
devices if something unexpected happens. In the nuclear industry, it is
the case of a Monte Carlo particle-transport program that requests users
to sign an agreement about the objective of its usage before allowing
its execution. The software itself might be open source because the
source code is provided after signing the agreement, but it is not free
(as in freedom) at all.

  [GNU General Public License]: https://www.gnu.org/licenses/gpl-3.0
  [the documentation]: https://seamplex.com/feenox/doc/
  [Creative Commons Attribution-ShareAlike 4.0 International License]: https://creativecommons.org/licenses/by-sa/4.0/
  [AGPL]: https://en.wikipedia.org/wiki/GNU_Affero_General_Public_License

Why is FeenoX written in C and not in…

See the programming guide for further discussion.

  [programming guide]: https://seamplex.com/feenox/doc/programming.html

C++?

Let us first start with some generalities

Why is C still in use even though we have C++?

    https://www.quora.com/Why-is-C-still-in-use-even-though-we-have-C++-Is-there-anything-that-C-can-do-but-C++-cant-or-maybe-something-that-is-easier-to-do-in-C-rather-than-C++

As a C programmer, why didn’t you switch to C++ in your career?

    https://qr.ae/pGzfAO

Why is PETSc programmed in C, instead of Fortran or C++?

    C enables us to build data structures for storing sparse matrices,
    solver information, etc. in ways that Fortran simply does not allow.
    ANSI C is a complete standard that all modern C compilers support.
    The language is identical on all machines. C++ is still evolving and
    compilers on different machines are not identical. Using C function
    pointers to provide data encapsulation and polymorphism allows us to
    get many of the advantages of C++ without using such a large and
    more complicated language. It would be natural and reasonable to
    have coded PETSc in C++; we opted to use C instead.

    https://www.mcs.anl.gov/petsc/documentation/faq.html#why-c

Why Git is written in C and not in C++, by Linus Torvalds

    C++ is a horrible language. It’s made more horrible by the fact that
    a lot of substandard programmers use it, to the point where it’s
    much much easier to generate total and utter crap with it. Quite
    frankly, even if the choice of C were to do nothing but keep the C++
    programmers out, that in itself would be a huge reason to use C.

    http://harmful.cat-v.org/software/c++/linus

In particular, I think that even though object-oriented programming does
provide a heck of a paradigm (hey, I actually rewrote my Blackjack
engine in C++ from its first version in C), it might subtly “force”
people to do stuff that is either way too

- convoluted
- artificial
- hard to debug
- long to compile

I nevertheless think that

- std containers are pretty cool
- templating can give and edge on some cases
- sometimes OOP may be a better approach to the Unix rule of
  representation (sometimes)

However, the pros of C++ do not outweigh its cons for a cloud-first
finite-elementish tool. Also, the name C++ is lame.

  [Blackjack engine]: https://www.seamplex.com/blackjack/

Fortran?

Because I am not insane (yet). I do not know any sane person that would
start writing a piece of software from scratch using Fortran in the 21st
century AD.

Python or R?

Python was not designed to perform actual computations but to add
another layer so as to ease some (and only some) tasks. The actual
computations are written in low-level languages, not in Python (nor
Octave, R, etc.) And even if it was, I would not choose a language where
scope depends on the indentation.

Go, Rust or Julia?

I don’t know them in detail so I cannot tell if any of these languages
would be a good fit for FeenoX. Keep in mind that it took me a while to
know why not Fortran nor C++ even though there are people that would
choose them over C. Maybe something of the sort happens with these new
ideas (or not, I don’t know).