How to install the latest Octave

This PPA 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 

The answer is quite simple. Go to the Octave downloads website and find the latest release of GNU Octave and download the .tar.gz file of it.

After this copy and paste the following terminal (CTRL+ALT+T) commands:

sudo apt-get build-dep octave
cd ~/Downloads
sudo mv octave-x.x.x.tar.gz ~
cd ~
tar xvf octave-x.x.x.tar.gz
cd octave-x.x.x
./configure
make
sudo make install

Where the 'x.x.x' refers to the version of GNU Octave you'd like to install, such as 3.6.3.

Just as an update: this PPA (maintained by a member of the Debian Octave Group) provides the latest Octave for a range of Ubuntu versions.