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I have modified scientific open-source code licensed with the GPLv3 license. If I run some simulations on my PC with this modified code and later on I want to publish a paper with the results of my simulations, would this be considered "conveying" according to the GNUv3 definition (and therefore triggering the obligation to share the code under the same license)?

I am all for open source and sharing the work but as I will be having this discussion with my PhD advisor I want to know for certain which are our obligations or not.

3 Answers 3

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No, the output of a GPL-covered program is not covered by the same license as the source code, apart from very special cases.

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I'm in agreement with the answer of Federico Poloni and the answer of Anonymous M, but point out that you need to either keep the modified code to yourself or have the license extended to it.

While it is fine, theoretically, to keep the code to yourself, it might make any external verification of your results difficult and possibly call them in to question.

For results, in these times, that depend on particular computer code, it is frowned upon to keep that code confidential. How serious that "frowning" can be depends on the importance and significance of the results. So people are "encouraged" to publish code.

Your choice, of course, but be aware of the possible future effect.

There is a subtlety here, of course. The real question isn't whether your results trigger GPL, but whether the GPL license requires that you actually publish any and all modifications of GPL code, or can a person/entity make a modification and not publish it at all. If they do publish it is clearly GPLd, and a possible interpretation is that it is even if not published, but that would be moot. After all, you wouldn't be "licensing" the code to others if it is held close.

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    'For results, in these times, that depend on particular computer code, it is frowned upon to keep that code confidential' Oh how I wish that were true. Commented Feb 20, 2023 at 14:12
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    This is why many people say "don't use GPL" for academic code, and probably most people using GPL on their work don't realize most of the implications or subscribe to the heavy-handed approach of GPL.
    – Bryan Krause
    Commented Feb 20, 2023 at 15:17
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    @BryanKrause: It depends which "most people" you're talking about. Some of them take the (IMHO) extreme position that it is unethical to provide binaries or source code under any license prohibiting the modification of said binaries or code. Such restrictions are common in industry, and they were the motivation for creating the GPL in the first place. Other people take the (IMHO) more moderate position that the GPL is about reciprocity - "If I give you all this code for $0, the least you can do is share your improvements under the same terms."
    – Kevin
    Commented Feb 21, 2023 at 2:15
  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Academia Meta, or in Academia Chat. Comments continuing discussion may be removed.
    – cag51
    Commented Feb 22, 2023 at 3:19
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I'm not a lawyer, etc.

I've simply never heard of this being a problem or heard it suggested as a consideration.

The work you obtained under the terms of GPLv3 was the software you used. Your paper is not a combined work, derived work, what have you of that software, as long as the paper doesn't actually include code from that software. Any software you made based on the GPL code is those things.

If you write a paper reporting on results from software, but no code, you have no obligation related to the GPL regarding the paper. If you distribute your code separately to be checked, which as a subjective point I think you should as a matter of basic academic integrity, then that code is definitely covered under GPLv3 and you have the corresponding obligation to license it under those terms. I prefer not to license code via GPL myself but have had to for a few projects because of this dynamic.

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