This letter is the first in a series extending step-by-step the Modern Portfolio Theory. It is aimed at financial portfolio managers and risk managers.
We start with a choice piece: the internal correlation of a portfolio. This is the key variable determining the risk of financial crash.
Since Harry Markowitz, portfolio managers think they know the solution to their investments: choose the most diversified assets possible. In other words, zero cooperation, zero correlation.
But how do we measure the correlation? And furthermore, how do we measure it in real time?
