MarsSeed [1] filed a deletion request for viennacl [2]: Unused headers-only library; last released in 2016. [a]
Upstream abandoned all maintenance 5 years ago. [b] [a]: https://sourceforge.net/projects/viennacl/files [b]: https://github.com/viennacl/viennacl-dev [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/viennacl/
