Re: [eigen] Call for survey questions

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi!

On 25/06/2019 20.45, David Tellenbach wrote:
> > Is anyone currently working on this? Or willing to start working on it?
> I've collected some questions mentioned in this thread. As already said I would set up the survey. However, some time has passed and I just didn't find the time. But it's definitely on my list and I guess I can at least present a first draft in July (since I'm a student my obligations are heavily changing from time to time).

Great! No need to rush it, especially since you do it in your spare time.

> [...]
> > An alternative (or addition) to the survey would be to comb through open-source projects and -- if they use Eigen -- try to automatically analyze things like what modules are used, what language standard is used, etc (depending on the thoroughness this is probably more complicated than doing a survey).
> Thats an interesting idea. Do you think about crawling the major code hosting providers? The very different structure of individual project could make this very hard, though.

Yes, I don't assume it is simple. But I have no experience regarding this.

> > If someone wants to handle this survey, do you need help in any form? Or access to anything?
> Regarding your idea above, is there a way to see where Eigen is used as a submodule? Any guesses if this is the main way of including Eigen into other projects?

I think a lot of projects just use the version provided by the operating 
system (no idea how many). And probably some made a hard-copy of Eigen 
into their repository. Sub-moduling into git was not possible for quite 
a while (the official github-mirror has only existed since end of 2017, 
but there were several in-official mirrors before that).

To find projects using Eigen, my naïve idea would be to start by 
grepping the source code for `#include <Eigen/*>` (of course with all 
possible alternatives (e.g., some people use things like `# include 
"eigen3/Eigen/Dense"`). To make this remotely possible, this requires 
some API to directly grep through all public projects on several code 
hosters [1].
The list of positive hits (including dates of most recent commits, 
number of watchers, etc) alone would be interesting.
But if somebody really wants to dig into this:
 * Filter out duplicates/forks/...
 * Figure out which modules are included (problem: some people include 
<Eigen/Dense> but essentially just use <Eigen/Core>.
 * What build-system is used?
   * Any compile-flags? Specific target architectures? Etc.
 * When was Eigen first used by the project (requires bisecting the 
history)?
 * Does it depend on features which will get deprecated? (Perhaps 
requires downloading and compiling -- this can get arbitrarily complex)
   * With which versions of Eigen does it compile? With which C++ 
standards/compilers? ...
 * The sky is the limit ... :D


[1] Looks like github provides this:
https://github.com/search/advanced
A very simple query already gives gazillons of results:
https://github.com/search?l=&p=1&q=%22%23include+%3CEigen%2F%22+language%3AC%2B%2B&type=Code
Of course, this would need to be condensed to be usable.


Cheers,
Christoph



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