Variance gamma process

In the theory of stochastic processes, a part of the mathematical theory of probability, the variance gamma process (VG), also known as Laplace motion, is a Lévy process determined by a random time change. The process has finite moments distinguishing it from many Lévy processes. There is no diffusion component in the VG process and it is thus a pure jump process. The increments are independent and follow a Variance-gamma distribution, which is a generalization of the Laplace distribution.

Three sample paths of variance gamma processes (in resp. red, green, black)

There are several representations of the VG process that relate it to other processes. It can for example be written as a Brownian motion $W(t)$ with drift $\theta t$ subjected to a random time change which follows a gamma process $\Gamma (t;1,\nu )$ (equivalently one finds in literature the notation $\Gamma (t;\gamma =1/\nu ,\lambda =1/\nu )$ ):

X^{VG}(t;\sigma ,\nu ,\theta )\;:=\;\theta \,\Gamma (t;1,\nu )+\sigma \,W(\Gamma (t;1,\nu ))\quad .

An alternative way of stating this is that the variance gamma process is a Brownian motion subordinated to a Gamma subordinator.

Since the VG process is of finite variation it can be written as the difference of two independent gamma processes:[1]

X^{VG}(t;\sigma ,\nu ,\theta )\;:=\;\Gamma (t;\mu _{p},\mu _{p}^{2}\,\nu )-\Gamma (t;\mu _{q},\mu _{q}^{2}\,\nu )

where

\mu _{p}:={\frac {1}{2}}{\sqrt {\theta ^{2}+{\frac {2\sigma ^{2}}{\nu }}}}+{\frac {\theta }{2}}\quad \quad {\text{and}}\quad \quad \mu _{q}:={\frac {1}{2}}{\sqrt {\theta ^{2}+{\frac {2\sigma ^{2}}{\nu }}}}-{\frac {\theta }{2}}\quad .

Alternatively it can be approximated by a compound Poisson process that leads to a representation with explicitly given (independent) jumps and their locations. This last characterization gives an understanding of the structure of the sample path with location and sizes of jumps.[2]

On the early history of the variance-gamma process see Seneta (2000).[3]

Moments

The mean of a variance gamma process is independent of $\sigma$ and $\nu$ and is given by

E[X(t)]=\theta t

The variance is given as

Var[X(t)]=(\theta ^{2}\nu +\sigma ^{2})t

The 3rd central moment is

E[(X(t)-E[X(t)])^{3}]=(2\theta ^{3}\nu ^{2}+3\sigma ^{2}\theta \nu )t

The 4th central moment is

E[(X(t)-E[X(t)])^{4}]=(3\sigma ^{4}\nu +12\sigma ^{2}\theta ^{2}\nu ^{2}+6\theta ^{4}\nu ^{3})t+(3\sigma ^{4}+6\sigma ^{2}\theta ^{2}\nu +3\theta ^{4}\nu ^{2})t^{2}

Option pricing

The VG process can be advantageous to use when pricing options since it allows for a wider modeling of skewness and kurtosis than the Brownian motion does. As such the variance gamma model allows to consistently price options with different strikes and maturities using a single set of parameters. Madan and Seneta present a symmetric version of the variance gamma process.[4] Madan, Carr and Chang [1] extend the model to allow for an asymmetric form and present a formula to price European options under the variance gamma process.

Hirsa and Madan show how to price American options under variance gamma.[5] Fiorani presents numerical solutions for European and American barrier options under variance gamma process.[6] He also provides computer programming code to price vanilla and barrier European and American barrier options under variance gamma process.

Lemmens et al.[7] construct bounds for arithmetic Asian options for several Lévy models including the variance gamma model.

Applications to Credit Risk Modeling

The variance gamma process has been successfully applied in the modeling of credit risk in structural models. The pure jump nature of the process and the possibility to control skewness and kurtosis of the distribution allow the model to price correctly the risk of default of securities having a short maturity, something that is generally not possible with structural models in which the underlying assets follow a Brownian motion. Fiorani, Luciano and Semeraro[8] model credit default swaps under variance gamma. In an extensive empirical test they show the overperformance of the pricing under variance gamma, compared to alternative models presented in literature.

Simulation

Monte Carlo methods for the variance gamma process are described by Fu (2000).[9] Algorithms are presented by Korn et al. (2010).[10]

Simulating VG as Gamma time-changed Brownian Motion

Input: VG parameters $\theta ,\sigma ,\nu$ and time increments $\Delta t_{1},\dots \Delta t_{N}$ , where $\sum _{i=1}^{N}\Delta t_{i}=T.$
Initialization: Set X(0)=0.
Loop: For i = 1 to N:

Generate independent gamma $\Delta \,G_{i}\,\sim \Gamma (\Delta t_{i}/\nu ,\nu )$ , and normal $Z_{i}\sim {\mathcal {N}}(0,1)$ variates, independently of past random variates.
Return $X(t_{i})=X(t_{i-1})+\theta \Delta G_{i}+\sigma {\sqrt {\Delta G_{i}}}Z_{i}.$

Simulating VG as difference of Gammas

This approach[9][10] is based on the difference of gamma representation $X^{VG}(t;\sigma ,\nu ,\theta )\;=\;\Gamma (t;\mu _{p},\mu _{p}^{2}\,\nu )-\Gamma (t;\mu _{q},\mu _{q}^{2}\,\nu )$ , where $\mu _{p},\mu _{q},\nu$ are defined as above.

Input: VG parameters $\theta ,\sigma ,\nu ,\mu _{p},\mu _{q}$ ] and time increments $\Delta t_{1},\dots \Delta t_{N}$ , where $\sum _{i=1}^{N}\Delta t_{i}=T.$
Initialization: Set X(0)=0.
Loop: For i = 1 to N:

Generate independent gamma variates $\gamma _{i}^{-}\,\sim \,\Gamma (\Delta t_{i}/\nu ,\nu \mu _{q}),\quad \gamma _{i}^{+}\,\sim \,\Gamma (\Delta t_{i}/\nu ,\nu \mu _{p}),$ independently of past random variates.
Return $X(t_{i})=X(t_{i-1})+\Gamma _{i}^{+}(t)-\Gamma _{i}^{-}(t).$

Simulating a VG path by difference of gamma bridge sampling

To be continued ...

Variance Gamma as 2-EPT distribution

Under the restriction that ${\frac {1}{\nu }}$ is integer the Variance Gamma distribution can be represented as a 2-EPT Probability Density Function. Under this assumption it is possible to derive closed form vanilla option prices and their associated Greeks. For a comprehensive description see.[11]

References

Dilip Madan, Peter Carr, Eric Chang (1998). "The Variance Gamma Process and Option Pricing" (PDF). European FinanceReview. 2: 79–105.CS1 maint: uses authors parameter (link)
Kotz, Samuel; Kozubowski, Tomasz J.; Podgórski, Krzysztof (2001). The Laplace distribution and generalizations : a revisit with applications to communications, economics, engineering, and finance. Boston [u.a.]: Birkhäuser. ISBN 978-0817641665.
Eugene Seneta (2000). "The Early Years of the Variance–Gamma Process". In Michael C. Fu; Robert A. Jarrow; Ju-Yi J. Yen; Robert J. Elliott (eds.). Advances in Mathematical Finance. Boston: Birkhauser. ISBN 978-0-8176-4544-1.
Madan, Dilip B.; Seneta, Eugene (1990). "The Variance Gamma (V.G.) Model for Share Market Returns". Journal of Business. 63 (4): 511–524. doi:10.1086/296519. JSTOR 2353303.
Hirsa, Ali; Madan, Dilip B. (2003). "Pricing American Options Under Variance Gamma". Journal of Computational Finance. 7 (2): 63–80. doi:10.21314/JCF.2003.112.
Filo Fiorani (2004). Option Pricing Under the Variance Gamma Process. Unpublished dissertation. p. 380. SSRN 1411741. PDF.
Lemmens, Damiaan; Liang, Ling Zhi; Tempere, Jacques; De Schepper, Ann (2010), "Pricing bounds for discrete arithmetic Asian options under Lévy models", Physica A: Statistical Mechanics and Its Applications, 389 (22): 5193–5207, doi:10.1016/j.physa.2010.07.026
Filo Fiorani, Elisa Luciano and Patrizia Semeraro, (2007), Single and Joint Default in a Structural Model with Purely Discontinuous Assets, Working Paper No. 41, Carlo Alberto Notebooks, Collegio Carlo Alberto. URL PDF
Michael C. Fu (2000). "Variance-Gamma and Monte Carlo". In Michael C. Fu; Robert A. Jarrow; Ju-Yi J. Yen; Robert J. Elliott (eds.). Advances in Mathematical Finance. Boston: Birkhauser. ISBN 978-0-8176-4544-1.
Ralf Korn; Elke Korn & Gerald Kroisandt (2010). Monte Carlo Methods and Models in Finance and Insurance. Boca Raton, Fla.: Chapman and Hall/CRC. ISBN 978-1-4200-7618-9. (Section 7.3.3)
Sexton, C. and Hanzon,B.,"State Space Calculations for two-sided EPT Densities with Financial Modelling Applications", www.2-ept.com

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.

[MadanCarrChang-1] Dilip Madan, Peter Carr, Eric Chang (1998). "The Variance Gamma Process and Option Pricing" (PDF). European FinanceReview. 2: 79–105.CS1 maint: uses authors parameter (link)

[sktkkp-2] Kotz, Samuel; Kozubowski, Tomasz J.; Podgórski, Krzysztof (2001). The Laplace distribution and generalizations : a revisit with applications to communications, economics, engineering, and finance. Boston [u.a.]: Birkhäuser. ISBN 978-0817641665.

[Seneta2000-3] Eugene Seneta (2000). "The Early Years of the Variance–Gamma Process". In Michael C. Fu; Robert A. Jarrow; Ju-Yi J. Yen; Robert J. Elliott (eds.). Advances in Mathematical Finance. Boston: Birkhauser. ISBN 978-0-8176-4544-1.

[4] Madan, Dilip B.; Seneta, Eugene (1990). "The Variance Gamma (V.G.) Model for Share Market Returns". Journal of Business. 63 (4): 511–524. doi:10.1086/296519. JSTOR 2353303.

[5] Hirsa, Ali; Madan, Dilip B. (2003). "Pricing American Options Under Variance Gamma". Journal of Computational Finance. 7 (2): 63–80. doi:10.21314/JCF.2003.112.

[6] Filo Fiorani (2004). Option Pricing Under the Variance Gamma Process. Unpublished dissertation. p. 380. SSRN 1411741. PDF.

[Lemmens2010-7] Lemmens, Damiaan; Liang, Ling Zhi; Tempere, Jacques; De Schepper, Ann (2010), "Pricing bounds for discrete arithmetic Asian options under Lévy models", Physica A: Statistical Mechanics and Its Applications, 389 (22): 5193–5207, doi:10.1016/j.physa.2010.07.026

[8] Filo Fiorani, Elisa Luciano and Patrizia Semeraro, (2007), Single and Joint Default in a Structural Model with Purely Discontinuous Assets, Working Paper No. 41, Carlo Alberto Notebooks, Collegio Carlo Alberto. URL PDF

[Fu-9] Michael C. Fu (2000). "Variance-Gamma and Monte Carlo". In Michael C. Fu; Robert A. Jarrow; Ju-Yi J. Yen; Robert J. Elliott (eds.). Advances in Mathematical Finance. Boston: Birkhauser. ISBN 978-0-8176-4544-1.

[kkk2010-10] Ralf Korn; Elke Korn & Gerald Kroisandt (2010). Monte Carlo Methods and Models in Finance and Insurance. Boca Raton, Fla.: Chapman and Hall/CRC. ISBN 978-1-4200-7618-9. (Section 7.3.3)

[11] Sexton, C. and Hanzon,B.,"State Space Calculations for two-sided EPT Densities with Financial Modelling Applications", www.2-ept.com

Stochastic processes
Discrete time	Bernoulli process Branching process Chinese restaurant process Galton–Watson process Independent and identically distributed random variables Markov chain Moran process Random walk Loop-erased Self-avoiding Biased Maximal entropy
Continuous time	Additive process Bessel process Birth–death process pure birth Brownian motion Bridge Excursion Fractional Geometric Meander Cauchy process Contact process Continuous-time random walk Cox process Diffusion process Empirical process Feller process Fleming–Viot process Gamma process Geometric process Hawkes process Hunt process Interacting particle systems Itô diffusion Itô process Jump diffusion Jump process Lévy process Local time Markov additive process McKean–Vlasov process Ornstein–Uhlenbeck process Poisson process Compound Non-homogeneous Schramm–Loewner evolution Semimartingale Sigma-martingale Stable process Superprocess Telegraph process Variance gamma process Wiener process Wiener sausage
Both	Branching process Galves–Löcherbach model Gaussian process Hidden Markov model (HMM) Markov process Martingale Differences Local Sub- Super- Random dynamical system Regenerative process Renewal process Stochastic chains with memory of variable length White noise
Fields and other	Dirichlet process Gaussian random field Gibbs measure Hopfield model Ising model Potts model Boolean network Markov random field Percolation Pitman–Yor process Point process Cox Poisson Random field Random graph
Time series models	Autoregressive conditional heteroskedasticity (ARCH) model Autoregressive integrated moving average (ARIMA) model Autoregressive (AR) model Autoregressive–moving-average (ARMA) model Generalized autoregressive conditional heteroskedasticity (GARCH) model Moving-average (MA) model
Financial models	Binomial options pricing model Black–Derman–Toy Black–Karasinski Black–Scholes Chen Constant elasticity of variance (CEV) Cox–Ingersoll–Ross (CIR) Garman–Kohlhagen Heath–Jarrow–Morton (HJM) Heston Ho–Lee Hull–White LIBOR market Rendleman–Bartter SABR volatility Vašíček Wilkie
Actuarial models	Bühlmann Cramér–Lundberg Risk process Sparre–Anderson
Queueing models	Bulk Fluid Generalized queueing network M/G/1 M/M/1 M/M/c
Properties	Càdlàg paths Continuous Continuous paths Ergodic Exchangeable Feller-continuous Gauss–Markov Markov Mixing Piecewise deterministic Predictable Progressively measurable Self-similar Stationary Time-reversible
Limit theorems	Central limit theorem Donsker's theorem Doob's martingale convergence theorems Ergodic theorem Fisher–Tippett–Gnedenko theorem Large deviation principle Law of large numbers (weak/strong) Law of the iterated logarithm Maximal ergodic theorem Sanov's theorem Zero–one laws (Blumenthal, Borel–Cantelli, Engelbert–Schmidt, Hewitt–Savage, Kolmogorov, Lévy)
Inequalities	Burkholder–Davis–Gundy Doob's martingale Doob's upcrossing Kunita–Watanabe
Tools	Cameron–Martin formula Convergence of random variables Doléans-Dade exponential Doob decomposition theorem Doob–Meyer decomposition theorem Doob's optional stopping theorem Dynkin's formula Feynman–Kac formula Filtration Girsanov theorem Infinitesimal generator Itô integral Itô's lemma Karhunen–Loève_theorem Kolmogorov continuity theorem Kolmogorov extension theorem Lévy–Prokhorov metric Malliavin calculus Martingale representation theorem Optional stopping theorem Prokhorov's theorem Quadratic variation Reflection principle Skorokhod integral Skorokhod's representation theorem Skorokhod space Snell envelope Stochastic differential equation Tanaka Stopping time Stratonovich integral Uniform integrability Usual hypotheses Wiener space Classical Abstract
Disciplines	Actuarial mathematics Control theory Econometrics Ergodic theory Extreme value theory (EVT) Large deviations theory Mathematical finance Mathematical statistics Probability theory Queueing theory Renewal theory Ruin theory Signal processing Statistics System on Chip design Stochastic analysis Time series analysis Machine learning
List of topics Category