The repository cannot be cloned
The README suggests the repository should be cloned using this (or a very similar) command:
git clone git@gitlab.inria.fr:solverstack/ScalFMM.git
For an unregistered user, this fails with the following error:
Cloning into 'ScalFMM'...
git@gitlab.inria.fr: Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
Solution
In the README, advertise the HTTPS URL rather than the ssh URL:
sed -i 's|git@gitlab.inria.fr:|https://gitlab.inria.fr/|' README.md