The phrasing of this licensing is unclear but essentially the same as the original Fortran library <http://www.astrouw.edu.pl/~jskowron/cmplx_roots_sg/>:
The authors release the source codes associated with the Paper under terms > of the GNU Lesser General Public License version 2 or any later version, or > under the Apache License, Version 2.0 as well as under a "customary > scientific license", which implies that if this code was important in the > scientific process or for the results of your scientific work, we ask for > the appropriate citation of the Paper (Skowron & Gould 2012). Their wording seems to indicate dual licensing under LGPL 2 or Apache 2, which would mean that following the terms of either license gives the right to use the software. But then it throws in the "as well as under a 'customary scientific license'" clause, which completely muddies the waters. Does that mean that you may use the software if you follow the terms of LGPL 2 AND cite them OR follow the terms of Apache 2 AND cite them? Or that you may use the software if you follow the terms of LGPL 2 OR cite them OR follow the terms of Apache 2 and cite them? Under the former interpretation, it would be illegal to use this software as part of a derived work including any GPL libraries (which includes Julia in its default configuration) since the "customary scientific license" conflicts with the GPL, thereby making it impossible to comply with all terms required to be allowed to use the combined product. If the authors intended to require you to follow both the LGPL 2 and Apache 2 licenses, the situation may be even worse, since, IIRC, those licenses themselves conflict, so it would be impossible to satisfy the conditions required to be allowed to use the software at all. It seems like it may be necessary to contact the authors and request their clarification of the terms under which one may use their software. On Thu, May 5, 2016 at 3:05 PM, Steven G. Johnson <[email protected]> wrote: > > > On Thursday, May 5, 2016 at 10:24:53 AM UTC-4, Mosè Giordano wrote: >> >> This package is licensed under Apache License 2.0 or GNU Lesser General >> Public License version 3 or any later version, as well as under a >> "customary scientific license", which implies that if this code was >> important in the scientific process or for the results of your scientific >> work, you are asked for the appropriate citation of the paper Skowron & >> Gould 2012 (http://arxiv.org/abs/1203.1034). >> > > It's a really bad idea to imply that citation is a legal requirement in > the license. Such a requirement makes your code non free/open-source > software. > > The best approach is to simply make a polite request, but be explicit that > it is not a legal requirement. In practice, people will happily comply > with such a request in my experience. e.g. this is what we say for FFTW: > > In addition, we kindly ask you to acknowledge FFTW and its > authors in any program or publication in which you use FFTW. (You are not > *required* to do so; it is up to your common sense to decide whether you > want to comply with this request or not.) For general publications, we > suggest referencing: Matteo Frigo and Steven G. Johnson, “The design and > implementation of FFTW3,” *Proc. IEEE* *93* (2), 216–231 (2005). >
