Octave for Android
Direct Octave installation
You can directly install Octave in Termux using the repository by its-pointless.
wget https://its-pointless.github.io/setup-pointless-repo.sh sh setup-pointless-repo.sh apt install octave
However, graphics capabilities are not available with this approach.
Via some Linux distribution
Inside Termux in Android, you can install a Linux distribution like Debian, Ubuntu, Arch or Alpine (this consumes less disk space). Octave can be installed as descried in Octave for GNU/Linux from the distribution's respective package manager.
To use Octave's graphical capabilities, the installation of a desktop environment and the usage of a VNC Server is required. (Please add more information how to do this here.) On many android devices, only the graphics toolkit "gnuplot" is known to work. Several apps (e.g. Anlinux, Andronix) are available to easily install the Linux distribution of your choice, and setting up the desktop environment.
The Android app GNURoot Octave in the Google play store is built and maintained by Corbin Champion. However, note that these repositories have not been updated for several years. It is not part of the GNU Octave project. Thus please use the following GitHub pages for questions and bug reports:
The implementation has been done in close cooperation with the Octave developers and makes use of the Octave source code without essential changes. Thus, it is fully compatible with the versions of Octave on other platforms.
Some probably outdated build instructions for the older "octave4android" app: