  We propose a frustrated and disordered many-body model of a stockmarket in
which independent adaptive traders can trade a stock subject to the economic
law of supply and demand. We show that the typical scaling properties and the
correlated volatility arise as a consequence of the collective behavior of
agents: With their interaction they determine a price which in turn affects
their future way of investing. We introduce only one type of investors, since
they all share the same hope: They simply want to maximize the profit
minimizing the risk. The best utilization of resources occurs at a critical
point characterized by the transition between the excess-demand and the
excess-supply phases.
