Installing Octave 3.6.1 in Ubuntu 12.04

Step-by-step:

1. Add the following ppa to your repository 
$ sudo add-apt-repository ppa:picaso/octave
2. Update and Install the octave
$ sudo apt-get update && sudo apt-get install octave
3. Run the following command to update the package
sudo apt-get install liboctave-dev
4. Need additional packages? Here are the examples. You can find other packages depend on your needs.
$ sudo apt-get install octave-control octave-audio octave-signal octave-plot
5. Run Octave
$ octave -q 

For GNU Octave 4.0, and 4.0.1 you can follow the following procedure.