# What do angle brackets ($\langle\rangle$ ) mean in mathematics/statistics (autocorrelations)?

Okay, so the logarithmic return on a stock is given by:

$$r_τ (t) = \ln P(t+τ) - \ln P(t),$$ where τ is the interval of time.

I have no problem calculating that. My question comes to the following formula:

$$ρ(T) \sim 〈r_τ (t+T) \cdot r_τ (t)〉$$

This is supposedly the autocorrelation function of log-returns. What's the deal with the brackets?

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Not too sure about stocks, but the angular brackets commonly indicate expected value in statistics. Would that make sense in this context? – EuYu Apr 18 '13 at 3:56
In physics, it's suppose to be an inner product. math.stackexchange.com/questions/134156/… math.stackexchange.com/questions/173407/… – Roman Luštrik Aug 21 '13 at 13:38