# skfolio.measures.effective_number_assets ### skfolio.measures.effective_number_assets(weights) Compute the effective number of assets, defined as the inverse of the Herfindahl index. $$ N_{eff} = \frac{1}{\Vert w \Vert_{2}^{2}} $$ It quantifies portfolio concentration, with a higher value indicating a more diversified portfolio. * **Parameters:** **weights** *ndarray of shape (n_assets,)* : Weights of the assets. * **Returns:** **value** *float* : Effective number of assets. ### References * **[1]** “Banking and Financial Institutions Law in a Nutshell”. Lovett, William Anthony (1988)