“…In (4), z 1 , z 2 are two Wiener processes, ρ is the correlation factor between them, and √ V is the volatility of the stock price. In (5), θ is the long-run mean variance, κ is the speed of mean reversion( the rate at which V reverts to θ ) and σ v is the volatility (Standard deviation) of the volatility V .…”