我正在尝试安装 lammps 软件，但是更新时出现此错误：
E:The repository 'http://ppa.launchpad.net/gladky-anton/lammps/ubuntu artful Release' does not have a Release file.,
W:Updating from such a repository can't be done securely, and is therefore disabled by default.,
W:See apt-secure(8) manpage for repository creation and user configuration details.,
W:Target Sources (main/source/Sources) is configured multiple times in /etc/apt/sources.list.d/kubuntu-ci-ubuntu-stable-artful.list:2 and /etc/apt/sources.list.d/kubuntu-ci-ubuntu-stable-artful.list:3
我输入：
sudo add-apt-repository ppa:gladky-anton/lammps
sudo apt-get update
但出现此错误：
Err:10 http://ppa.launchpad.net/gladky-anton/lammps/ubuntu artful Release
404 Not Found
N: Updating from such a repository can't be done securely, and is therefore disabled by default
E: The repository 'http://ppa.launchpad.net/gladky-anton/lammps/ubuntu artful
Release' does not have a Release file.
W: Target Sources (main/source/Sources) is configured multiple times in
/etc/apt/sources.list.d/kubuntu-ci-ubuntu-stable-artful.list:2 and
/etc/apt/sources.list.d/kubuntu-ci-ubuntu-stable-artful.list:3