  I find a topological arrangement of stocks traded in a financial market which
has associated a meaningful economic taxonomy. The topological space is a graph
connecting the stocks of the portfolio analyzed. The graph is obtained starting
from the matrix of correlation coefficient computed between all pairs of stocks
of the portfolio by considering the synchronous time evolution of the
difference of the logarithm of daily stock price. The hierarchical tree of the
subdominant ultrametric space associated with the graph provides information
useful to investigate the number and nature of the common economic factors
affecting the time evolution of logarithm of price of well defined groups of
stocks.
