As you may know, GNU Octave is an open-source, Matlab alternative. The software provide capabilities for numerical solution of linear and nonlinear problems and has graphics capabilities for data visualization and manipulation.
For now, GNU Octave was only a command-line interface application but starting with Octave 4.0.0, which has been recently released, it also got a GUI. Also, the software now uses OpenGL graphics with Qt widgets by default and a lot of new functions and options have been implemented. For more information about this software, read the changelog.
Octave 4.0 is not available via any repository or PPA and so, we need to install it from sources, which takes a lot of time and energy.
However, if you still want to proceed, you need to build the octave dependencies, download the octave*.tar.gz archive from GNU, extract it, cd into the extracted folde and run configure, make and make install:
$ sudo apt-get build-dep octave
$ wget ftp.gnu.org/gnu/octave/octave-4.0.0.tar.gz
$ tar xzvf octave-4.0.0.tar.gz
$ cd octave-4.0.0
$ sudo make install
By default, when you start octave, from either the terminal or by double-clicking the icon, it starts in the GUI mode.
For the command-line version of octave, start it like this:
$ octave --no-gui
I have tested the instructions on Ubuntu 15.04 Vivid Vervet and Ubuntu 14.04 Trusty Tahr, so the installation steps would most likely work on derivative systems like Linux Mint 17.2 Rafaela, Linux Mint 17.1 Rebecca, Linux Mint 17 Qiana, Pinguy OS 14.04, Elementary OS 0.3 Freya, Deepin 2014, Peppermint Five, LXLE 14.04 and Linux Lite 2.