  The dynamics of a stock market with heterogeneous agents is discussed in the
framework of a recently proposed spin model for the emergence of bubbles and
crashes. We relate the log returns of stock prices to magnetization in the
model and find that it is closely related to trading volume as observed in real
markets. The cumulative distribution of log returns exhibits scaling with
exponents steeper than 2 and scaling is observed in the distribution of
transition times between bull and bear markets.
