  Based on the minute-by-minute data of the Hang Seng Index in Hong Kong and
the analysis of probability distribution and autocorrelations, we find that the
index fluctuations for the first few minutes of daily opening show behaviors
very different from those of the other times. In particular, the properties of
tail distribution, which will show the power law scaling with exponent about -4
or an exponential-type decay, the volatility, and its correlations depend on
the opening effect of each trading day.
