You could be just 4 terminal commands away from an easy installation, depending on the state of your system.
First, there is always risk breaking from the herd. My 15.10 system only has python-matplotlib 1.4.1something or other.
You could download the source
Once you have satisfied the requirements detailed in the
INSTALL file (mainly python, numpy, libpng and freetype), you can build matplotlib.
sudo apt-get build-dep python-matplotlib to install all
dependecies required to build matplotlib
cd ~/Downloads/matplotlib because that is where you unpacked
python3 setup.py build
sudo python3 setup.py install
The instructions use default interpreter, I used python3 and mine built/installed without a hitch, your success will depend on the state of your system. Read the error logs. They will tell you what went wrong. Generally involving
sudo apt-get install <lib[some]-dev>, or pre-emptively,