##### Motivation for this change

<!-- please explain your reason for doing this change -->

##### Things done/to do

<!-- please fill in the following checklist -->
- [ ] added corresponding entries in `CHANGELOG_UNRELEASED.md`
- [ ] added corresponding documentation in the headers
<!-- Cross-out the above items using ~crossed out item~ if they happen not to be relevent -->
<!-- You may also add more items to explain what you did and what remains to do -->

<!-- leave this note as a reminder to reviewers -->
##### Automatic note to reviewers

Read [this Checklist](https://github.com/math-comp/math-comp/wiki/Checklist-for-following,-reviewing-and-playing-with-a-PR#checklist-for-reviewing-a-pr) and make sure there is a milestone.