Before revision:  We  find that the presence of more assets , the heterogeneity of trading skills (e.g. speed or cost), and a large number of agents make the market more prone to large oscillations and instability.
After revision:  We prove the existence and uniqueness of the corresponding Nash equilibria for the related mean-variance optimization problem. We find that the presence of more assets , the heterogeneity of trading skills (e.g. speed or cost), and a large number of agents make the market more prone to large oscillations and instability.