  We propose a methodology for clustering financial time series of stocks'
returns, and a graphical set-up to quantify and visualise the evolution of
these clusters through time. The proposed graphical representation allows for
the application of well known algorithms for solving classical combinatorial
graph problems, which can be interpreted as problems relevant to portfolio
design and investment strategies. We illustrate this graph representation of
the evolution of clusters in time and its use on real data from the Madrid
Stock Exchange market.
