[Dune] license again

[Gregor Corbin]

Dear Dune Community,

as part of my Ph.D. I wrote some code based on DUNE and DUNE PDELab, 
which I now want make accessible for everyone. I sent everything (the 
research code, auxiliary scripts, outputs) to the university library to 
put it on one of their servers.
They asked me under which license I want to publish it. My first 
instinct was to choose a relatively strict open source license, such as 
GPL. But I have really no clue about the fine details and implications.
The person from the library told me that using the GPL could mean that 
colleagues from my work group could not re-use my code for their 
research/publications. This seems a bit far fetched for me, as there is 
apparently also no problem for me to publish results obtained with code 
based on the Dune libraries.

So, are there any downsides of using the GPL?

To complicate matters, I included a small patch (as a git diff) to 
dune-geometry (The original dune modules are not a part of the published 
package. I only have a script to clone them from their repositories). 
Does this mean I have to use the GPL anyway? I am aware that there was a 
discussion about licenses to modified dune code recently, but this is 
still unclear to me.

I would be grateful for any advice in this.

Cheers,
Gregor Corbin