A question on licenses

[Simon Sticko]

Hi.

The function

GridIn::read_msh

uses the Gmsh-api internally to read a mesh from file.  However, Gmsh is distributed under GPL and not LGPL.

Does this mean that one can not use this function if one wants to use deal.II under LGPL?

Best,

Simon

[Matthias Maier]

[Standard bla bla: I am not a lawyer]

Generally speaking, yes.

If you happen to use deal.II with any of the GPL only derivatives (such
as GMSH, or more importantly, P4est) then the "effective" license for
deal.II would be GPL [1,2,3].

But generally this is only of concern if you

- distribute deal.II in binary form. In this case the effective license
of deal.II is GPL (and not LGPL) and you have to abide to the rules
of the more restrictive license (by making all source code of deal.II
and all GPL dependencies available).

- distribute your own project based on deal.II in binary form. In this
case the GPL license would apply to deal.II and your project and
would require you to make your source code available to *everyone who
received your binary program*.

* In general you are neither required to publish your project, nor to
make source code available except in the case(s) outlined above.

Best,
Matthias



[1] This has funny consequences: If one of the dependencies is licensed
under GPL-2 only and another one is GPL-3 only then you would be unable
to the resulting library/executable in binary form... the licenses are
incompatible.



[2] Sometimes a GPL only project contains a "linkage exception" to work
around this issue. And sure enough GMSH has one:

Gmsh is provided under the terms of the GNU General Public License
(GPL), Version 2 or later, with the following exception:

The copyright holders of Gmsh give you permission to combine Gmsh
with code included in the standard release of Netgen (from Joachim
Sch"oberl), METIS (from George Karypis at the University of
Minnesota), OpenCASCADE (from Open CASCADE S.A.S) and ParaView
(from Kitware, Inc.) under their respective licenses. You may copy
and distribute such a system following the terms of the GNU GPL for
Gmsh and the licenses of the other code concerned, provided that
you include the source code of that other code when and as the GNU
GPL requires distribution of source code.

Note that people who make modified versions of Gmsh are not
obligated to grant this special exception for their modified
versions; it is their choice whether to do so. The GNU General
Public License gives permission to release a modified version
without this exception; this exception also makes it possible to
release a modified version which carries forward this exception.


I have no idea why the GMSH authors haven't used one of the standard
linkage exceptions that would apply to everyone and decided on this very
specific wording...