Hierarchical structure in financial markets

I find a hierarchical arrangement of stocks traded in a financial market by investigating the daily time series of the logarithm of stock price. The t opological space is a subdominant ultrametric space associated with a graph connecting the stocks of the portfolio analyzed. The graph is obtained sta rting from the matrix of correlation coefficient computed between all pairs of stocks of the portfolio by considering the synchronous time evolution o f the difference of the logarithm of daily stock price. The hierarchical tr ee of the subdominant ultrametric space associated with the graph provides a meaningful economic taxonomy.