我正在尝试在新安装的 Ubuntu 16.04 上安装八度音程。所以我试过这些命令：
sudo apt-add-repository ppa:octave/stable
sudo apt-get update
sudo apt-get install octave
在“sudo apt-get update”之后，我收到了以下错误和警告：
Err:9 http://ppa.launchpad.net/octave/stable/ubuntu xenial/main amd64 Packages
404 Not Found
Err:10 http://ppa.launchpad.net/octave/stable/ubuntu xenial/main i386 Packages
404 Not Found
W: The repository 'http://ppa.launchpad.net/octave/stable/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://ppa.launchpad.net/octave/stable/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found …