Question: I want to install Octave on my Ubuntu LTS with `apt-get`. The problem is that the official repositories list only Octave 3.0 and Octave 3.2, whereas the latest Octave is Octave 3.6.

How do I update the repositories of apt-get to get Octave 3.6?

Answer: 
[This PPA](https://launchpad.net/%7Epicaso/+archive/octave) should solve your problem, provided you are running the latest 12.04.

Open Terminal `Ctrl-Alt-T` and type:

```

sudo apt-add-repository -y ppa:picaso/octave
sudo apt-get update 
sudo apt-get install octave
sudo apt-get install liboctave-dev 

```

---

For Ubuntu 20.04, see [this](https://askubuntu.com/a/206050/124466) answer.
I am only "answering" this because I could not format in the comments. kudos to @izx and @Brenton Horne

For 14.0.4.2, I had to use a bit of both answers:

```
sudo apt-add-repository -y ppa:picaso/octave
sudo apt-get update
sudo apt-get install octave
sudo apt-get install liboctave-dev

```

These made octave 4.0 run, but not with `--force-gui`

```
sudo apt-get build-dep octave

```

was also required to get `--force-gui` to work.