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In finance, the Heston model, named after Steven L. Heston, is a mathematical model that describes the evolution of the volatility of an underlying asset. [1] It is a stochastic volatility model: such a model assumes that the volatility of the asset is not constant, nor even deterministic, but follows a random process.
Volatility risk is the risk of an adverse change of price, due to changes in the volatility of a factor affecting that price. It usually applies to derivative instruments , and their portfolios, where the volatility of the underlying asset is a major influencer of option prices .
actual historical volatility which refers to the volatility of a financial instrument over a specified period but with the last observation on a date in the past near synonymous is realized volatility , the square root of the realized variance , in turn calculated using the sum of squared returns divided by the number of observations.
Portfolio return volatility is a function of the correlations ρ ij of the component assets, for all asset pairs (i, j). The volatility gives insight into the risk which is associated with the investment. The higher the volatility, the higher the risk. In general: Expected return:
The implied volatility smile refers to the pattern of implied volatilities for options contracts with the same expiration date but different strike prices. The slope of the implied volatility smile reflects the market's expectations for future changes in the stock price, with a steeper slope indicating higher expected volatility.
The investor's utility function is concave and increasing, due to their risk aversion and consumption preference. Analysis is based on single period model of investment. An investor either maximizes their portfolio return for a given level of risk or minimizes their risk for a given return. [2] An investor is rational in nature.
The parameter corresponds to the speed of adjustment to the mean , and to volatility. The drift factor, a ( b − r t ) {\displaystyle a(b-r_{t})} , is exactly the same as in the Vasicek model. It ensures mean reversion of the interest rate towards the long run value b {\displaystyle b} , with speed of adjustment governed by the strictly ...
The volatility of volatility controls its curvature. The above dynamics is a stochastic version of the CEV model with the skewness parameter β {\displaystyle \beta } : in fact, it reduces to the CEV model if α = 0 {\displaystyle \alpha =0} The parameter α {\displaystyle \alpha } is often referred to as the volvol , and its meaning is that of ...