A probabalility question

You have N balls with N different colors. Randomly you draw two at a time,
then painting the first ball to match the second. What is the expected
number of drawings before all balls are the same color?

from MATLAB to Python/NumPy

Recently I started to translate the
MATLAB and Octave Functions for Computer Vision and Image Processing.
by Peter Kovesi into a Python package.
See
http://cvgmi.googlecode.com/files/fundamental_matrix.py

Python tips and tricks

Q: How to add current path into system?
A: sys.path.append(os.path.abspath('./'))