How to install octave 4.2.0 on my machine?

How can I install Octave 4.2.0 or latest? I have tried: - Installing latest version of GNU Octave when I have already installed other version : does not give flathub command not found - Installing Octave 4.2.0 from source on ubuntu? : does not work - Installing Octave 4.2.0 from source on ubuntu? : does not work configure: error: BLAS and LAPACK libraries are required - Installing Octave 4.2.0 from source on ubuntu? : not work installed 4.0.3 instead This is my PC version: $ lsb_release -a No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux 9.6 (stretch) Release: 9.6 Codename: stretch I ran the command sudo -i to enter root then the following commands. I am not sure if it is correct. $ sudo -i # echo deb http://deb.debian.org/debian stretch-backports main > /etc/apt/sources.list.d/stretch-backports.list # apt update Ign:1 http://deb.debian.org/debian stretch InRelease Hit:2 http://security.debian.org stretch/updates InRelease Hit:3 http://deb.debian.org/debian stretch-updates InRelease Hit:4 http://deb.debian.org/debian stretch-backports InRelease Hit:5 http://deb.debian.org/debian stretch Release Hit:7 http://packages.cloud.google.com/apt cloud-sdk-stretch InRelease Hit:8 https://download.docker.com/linux/debian stretch InRelease Hit:9 https://nvidia.github.io/libnvidia-container/debian9/amd64 InRelease Hit:10 http://packages.cloud.google.com/apt google-compute-engine-stretch-stable InRelease Hit:11 https://nvidia.github.io/nvidia-container-runtime/debian9/amd64 InRelease Hit:12 http://packages.cloud.google.com/apt google-cloud-packages-archive-keyring-stretch InRelease Hit:6 https://packages.cloud.google.com/apt kubernetes-xenial InRelease Ign:13 http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu disco InRelease Hit:14 https://nvidia.github.io/nvidia-docker/debian9/amd64 InRelease Ign:16 http://ppa.launchpad.net/octave/stable/ubuntu disco InRelease Ign:17 http://ppa.launchpad.net/picaso/octave/ubuntu disco InRelease Err:18 http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu disco Release 404 Not Found Err:19 http://ppa.launchpad.net/octave/stable/ubuntu disco Release 404 Not Found Err:20 http://ppa.launchpad.net/picaso/octave/ubuntu disco Release 404 Not Found Reading package lists... Done W: Target Packages (main/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target DEP-11 (main/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1W: Target DEP-11-icons (main/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 E: The repository 'http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu disco Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. E: The repository 'http://ppa.launchpad.net/octave/stable/ubuntu disco Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. E: The repository 'http://ppa.launchpad.net/picaso/octave/ubuntu disco Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. W: Target Packages (main/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target DEP-11 (main/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1 W: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1W: Target DEP-11-icons (main/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list.d/backports.list:1 and /etc/apt/sources.list.d/stretch-backports.list:1