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[Help-gsl] Licensing

From: Jonny Taylor
Subject: [Help-gsl] Licensing
Date: Mon, 14 Jun 2010 17:02:53 +0100

Hi all,

Hopefully somebody can help me clarify some licensing issues with some code of 
mine that links against GSL. I have never had to worry about licensing before, 
and I am finding even the FAQ for the GPL license rather impenetrable!

My situation is that I have code developed in the course of my university 
research that I would like to release for (slightly!) wider consumption. Being 
a relatively large project is links against a number of libraries:

1. My own code, written from scratch
links against
2. Apple system libraries (e.g. Accelerate, QuickTime)
3. GSL (GPL license)
4. GMP multiple precision math library (LGPL license)
5. Custom matrix eigenvalue library (explained below)
6. My own support library, written from scratch

#5 is a library I have hacked together from the GSL sources, where a copy of 
the GSL matrix eigenvalue code (and all its dependencies) has been modified to 
use GMP high precision arithmetic in order to solve a particularly awkward 
eigenvalue problem that suffers from catastrophic cancelation. I have no 
objection to releasing this library under whatever license might be necessary 
(though it was such a crude plugging together of two sets of code that I doubt 
anybody would be interested!). This library code is only of very peripheral 
relevance to the main project, and could be released as an entirely separate 
program if that opened up more licensing options for the main code.

My understanding is that simply by linking #1 against #3 (GSL), even 
dynamically linking, then I have restricted myself to the simple choice - 
release all of my code (#1) under the GPL, or do not release it at all. My 
reading is that I cannot even use LGPL for my code, for example, but must use 
GPL (version 3 or greater). If somebody was able to confirm whether I'm right 
there, that would be very helpful. Without wishing to wind anybody up, as 
somebody who knows basically nothing about licensing I find that rather 
surprising. If that's the case, though, fair enough.

Assuming I am right with that, as far as I can tell there is no additional 
issue raised by #5. I just leave the GPLv3 header at the top of the files in #5 
with a note that I have hacked them about, but the presence of this modified 
code does not have any further impact given that I have to use the GPL anyway. 
I think I can use whatever license I want for #6 (for what it's worth) as long 
as it is compatible with the GPL in the sense that it enables #1, which it 
seems must be GPLv3, to link against #6.

Thanks very much to anybody who has waded through all that - any comments would 
be very welcome.

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