How to: Sum, Mean, Variance, Covariance in Linear Algebra

If the title looks puzzling let me say that I believe that learning Python (or R) will take you to Machine Learning, but learning Linear Algebra will take you everywhere.

So going from using sw libraries to creating your stuff means moving with agility from numbers to vectors (and matrices) and often translating “Summations” expressions into equivalent one shot Vector/Matrix operations.

Unfortunately moving between these two worlds has some traps for beginners that might be good to refresh as they come up…