/usr/share/man/man3/dsysv.3.gz is in liblapack-doc 3.7.1-4ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man3/doubleSYsolve.3.gz
/usr/share/man/man3/doubleSYsolve.3.gz