Prediction of linear fractional stable motions using codifference, with application to non-Gaussian rough volatility
Pith reviewed 2026-05-19 04:22 UTC · model grok-4.3
The pith
A codifference-based predictor forecasts increments of linear fractional stable motions, separating kurtosis from serial dependence in rough volatility.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors show that the codifference fully characterizes the dependence structure of the linear fractional stable motion for the purpose of prediction, yielding forecasts that account for both the stable distribution of increments and their fractal dependence; this decomposition is demonstrated to be effective when the method is applied to time series of realized volatilities.
What carries the argument
The codifference, which quantifies dependence between stable random variables without requiring finite second moments, used to construct a conditional predictor or projection for future LFSM increments from past observations.
If this is right
- The method isolates the contribution of heavy tails from long-memory effects inside the fractal dynamics of rough volatility.
- A selective-memory regime of serial dependence appears for fractional processes, distinct from independence, persistence, and antipersistence.
- The predictor applies to any alpha-stable increment process by switching between conditional expectation and semimetric projection according to the value of alpha.
- Forecast accuracy improves relative to covariance-based methods once variance becomes infinite.
Where Pith is reading between the lines
- The same codifference construction could be tested on other heavy-tailed long-memory series such as trading volumes or energy prices.
- Risk-management applications might benefit from the explicit separation of tail behavior and persistence when setting volatility forecasts.
- Empirical confirmation of the selective-memory regime would require hit-ratio studies on additional asset classes and time scales.
Load-bearing premise
Real volatility series can be treated as discrete observations of a linear fractional stable motion with constant parameters, and the codifference supplies all information needed for accurate conditional prediction.
What would settle it
On a fresh out-of-sample volatility dataset the codifference-based LFSM forecasts would show no advantage over fractional Brownian motion forecasts or would fail to separate the kurtosis contribution from the dependence contribution.
Figures
read the original abstract
The linear fractional stable motion (LFSM) extends the fractional Brownian motion (fBm) by considering $\alpha$-stable increments. We propose a method to forecast future increments of the LFSM from past discrete-time observations, using the conditional expectation when $\alpha>1$ or a semimetric projection otherwise. It relies on the codifference, which describes the serial dependence of the process, instead of the covariance. Indeed, covariance is commonly used for predicting an fBm but it is infinite when $\alpha<2$. Some theoretical properties of the method and of its accuracy are studied and both a simulation study and an application to real volatility data, with a comparison to the fBm and to the heterogeneous auto-regressive model, confirm the relevance of the approach. The LFSM-based method shows a promising performance in the forecast of time series of volatilities, decomposing properly, in the fractal dynamic of rough volatilities, the contribution of the kurtosis of the increments and the contribution of their serial dependence. Moreover, the analysis of hit ratios suggests that, beside independence, persistence, and antipersistence, a fourth regime of serial dependence exists for fractional processes, characterized by a selective memory controlled by a few large increments.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a forecasting method for increments of linear fractional stable motion (LFSM) that replaces covariance with the codifference, using conditional expectation when α>1 and a semimetric projection otherwise. It derives some theoretical properties of the predictor and its accuracy, presents a simulation study, and applies the approach to real volatility time series, comparing performance against fractional Brownian motion and the heterogeneous autoregressive (HAR) model. The central claims are that the LFSM-based predictor decomposes the fractal dynamics of rough volatility into separate contributions from increment kurtosis and serial dependence, yields promising forecast accuracy, and reveals a fourth regime of serial dependence (selective memory controlled by large increments) beyond independence, persistence, and antipersistence.
Significance. If the codifference is shown to determine the relevant conditional distributions and if a single LFSM with time-invariant parameters adequately approximates discrete volatility observations, the work would supply a concrete non-Gaussian extension of rough-volatility forecasting that separates heavy-tail effects from long-memory effects. The simulation and empirical comparisons, together with the identification of a potential fourth dependence regime, would then constitute a useful methodological contribution to statistical modeling of financial time series.
major comments (3)
- [Theoretical properties] Theoretical properties section: the claim that the codifference fully characterizes the serial dependence structure needed for optimal conditional prediction is load-bearing for the method; however, for α-stable processes the codifference is a pairwise measure and does not necessarily determine the full finite-dimensional distributions, so tail dependence or higher-order stable integrals could affect forecast accuracy (see also the definition of the predictor via conditional expectation or semimetric projection).
- [Application to real volatility data] Application to real volatility data: the modeling assumption that discrete volatility observations are well-approximated by an LFSM with constant α and H is central to the reported performance gains and to the decomposition of kurtosis versus serial dependence; yet rough-volatility series typically exhibit time-varying Hurst exponents, volatility clustering, and leverage effects that violate strict self-similarity and stationary-increments, and no diagnostic or robustness check against these violations is described.
- [Simulation study] Simulation study: the reported gains over fBm and HAR are presented at high level only; without explicit information on parameter estimation procedures, cross-validation, or controls for post-hoc tuning, it is unclear whether the performance differences are robust or could be affected by data selection.
minor comments (2)
- [Abstract] Abstract: the phrase 'some theoretical properties of the method and of its accuracy are studied' is vague; a brief indication of the main result (e.g., consistency or an error bound) would help readers assess the strength of the theoretical contribution.
- [Method] Notation: the precise definition of the semimetric projection used when α ≤ 1 should be stated explicitly, including any normalization or choice of metric, to allow reproducibility.
Simulated Author's Rebuttal
We thank the referee for their thorough review and valuable suggestions. We have carefully considered each comment and provide point-by-point responses below. Revisions have been made to enhance the manuscript's clarity and address the raised concerns.
read point-by-point responses
-
Referee: Theoretical properties section: the claim that the codifference fully characterizes the serial dependence structure needed for optimal conditional prediction is load-bearing for the method; however, for α-stable processes the codifference is a pairwise measure and does not necessarily determine the full finite-dimensional distributions, so tail dependence or higher-order stable integrals could affect forecast accuracy (see also the definition of the predictor via conditional expectation or semimetric projection).
Authors: We acknowledge that the codifference, being a pairwise measure, does not fully characterize the finite-dimensional distributions of α-stable processes, and higher-order dependencies could influence predictions. However, our predictor is specifically constructed within the LFSM framework using the codifference to generalize the covariance-based approach for fBm. The theoretical properties we derive hold under the LFSM model assumptions. In the revised manuscript, we have added a paragraph discussing this limitation and clarifying that the method focuses on capturing the relevant dependence for forecasting increments via the defined projection or conditional expectation. revision: partial
-
Referee: Application to real volatility data: the modeling assumption that discrete volatility observations are well-approximated by an LFSM with constant α and H is central to the reported performance gains and to the decomposition of kurtosis versus serial dependence; yet rough-volatility series typically exhibit time-varying Hurst exponents, volatility clustering, and leverage effects that violate strict self-similarity and stationary-increments, and no diagnostic or robustness check against these violations is described.
Authors: We agree that the LFSM with time-invariant parameters is an approximation and that real volatility data may exhibit time-varying Hurst exponents, clustering, and leverage effects. Our goal is to demonstrate how the LFSM can separate the effects of kurtosis and serial dependence in a fractal setting. To address this, we have included in the revision a section with robustness checks, such as parameter stability analysis over subsamples and a discussion of potential model misspecification. revision: yes
-
Referee: Simulation study: the reported gains over fBm and HAR are presented at high level only; without explicit information on parameter estimation procedures, cross-validation, or controls for post-hoc tuning, it is unclear whether the performance differences are robust or could be affected by data selection.
Authors: We appreciate the referee's point regarding the simulation study details. The original submission summarized the results at a high level to focus on the main findings. In the revised version, we have expanded this section to provide full details on the parameter estimation procedure (based on codifference matching), the cross-validation scheme for out-of-sample forecasting, and additional sensitivity analyses across various parameter configurations to confirm the robustness of the performance gains. revision: yes
Circularity Check
No significant circularity; predictor relies on external codifference definition and conditional expectation
full rationale
The forecasting procedure is constructed from the standard definition of codifference for α-stable processes and the conditional expectation (or semimetric projection) operator, both of which are independent of the target volatility dataset. Parameter estimation for α and H occurs upstream of the predictor and does not make the subsequent forecast equivalent to the fitted values by construction. Theoretical properties, simulation comparisons, and real-data hit-ratio analysis supply independent content. No load-bearing step reduces the claimed decomposition of kurtosis versus serial dependence to a renaming or self-referential fit.
Axiom & Free-Parameter Ledger
free parameters (2)
- stability parameter alpha
- Hurst index H
axioms (1)
- domain assumption The process is a linear fractional stable motion with stationary increments.
Reference graph
Works this paper leans on
-
[1]
E. Abi Jaber and N. De Carvalho. Reconciling rough volatility with jumps. SIAM journal on financial mathematics, 15(3):785–823, 2024
work page 2024
-
[2]
E. Abi Jaber and S. Li. Volatility models in practice: rough, path-dependent, or markovian? To appear in Mathematical finance, 2025
work page 2025
-
[3]
M. Alfeus, M.M. Mwampashi, C.S. Nikitopoulos, and L. Overbeck. Stochastic modelling and forecasting of wind capacity utilization with applications to risk management: The Australian case. Pacific-basin finance journal, 91:102769, 2025
work page 2025
-
[4]
E. Al` os, J.A. Le´ on, and J. Vives. On the short-time behavior of the implied volatility for jump- diffusion models with stochastic volatility. Finance and stochastics, 11(4):571–589., 2007
work page 2007
-
[5]
A. Ammy-Driss and M. Garcin. Efficiency of the financial markets during the COVID-19 crisis: time-varying parameters of fractional stable dynamics. Physica A: statistical mechanics and its applications, 609:128335, 2023
work page 2023
-
[6]
A. Ayache and J. Hamonier. Linear fractional stable motion: A wavelet estimator of the α parameter. Statistics & probability letters , 82(8):1569–1575, 2012
work page 2012
-
[7]
L. Belkacem, J. L´ evy V´ ehel, and C. Walter. CAPM, risk and portfolio selection in α-stable markets. Fractals, 8(1):99–115, 2000
work page 2000
-
[8]
S. Bianchi, A. Pantanella, and A. Pianese. Modeling stock prices by multifractional Brownian motion: an improved estimation of the pointwise regularity. Quantitative finance, 13(8):1317– 1330, 2013
work page 2013
-
[9]
M. Bibinger, J. Yu, and C. Zhang. Modeling and forecasting realized volatility with multi- variate fractional Brownian motion. arXiv preprint, 2025
work page 2025
-
[10]
M. Bohdalov´ a and M. Greguˇ s. Fractal analysis of forward exchange rates.Acta polytechnica hungarica, 7(4):57–69, 2010
work page 2010
-
[11]
X. Brouty and M. Garcin. Fractal properties, information theory, and market efficiency.Chaos, solitons & fractals , 180:114543, 2024
work page 2024
-
[12]
M.E. ¸ Cek. Covert communication using skewed α-stable distributions. Electronics letters, 51(1):116–118, 2015
work page 2015
-
[13]
M.E. ¸ Cek and F.A. Savaci. Stable non-Gaussian noise parameter modulation in digital com- munication. Electronics letters, 45(24):1256–1257, 2009
work page 2009
-
[14]
J.M. Chambers, C.L. Mallows, and B.W. Stuck. A method for simulating stable random variables. Journal of the American statistical association , 71(354):340–344, 1976
work page 1976
-
[15]
A.V. Chechkin and V.Y. Gonchar. A model for persistent L´ evy motion. Physica A: statistical mechanics and its applications , 277(3-4):312–326, 2000
work page 2000
- [16]
-
[17]
P. Cheridito, H. Kawaguchi, and M. Maejima. Fractional Ornstein-Uhlenbeck processes. Elec- tronic journal of probability , 8(3):1–14, 2003. 22
work page 2003
-
[18]
J.-F. Coeurjolly. Simulation and identification of the fractional Brownian motion: a biblio- graphical and comparative study. Journal of statistical software , 5:1–53, 2000
work page 2000
-
[19]
F. Comte and E. Renault. Long memory in continuous-time stochastic volatility models. Mathematical finance, 8(4):291–323, 1998
work page 1998
-
[20]
R. Cont and P. Das. Rough volatility: fact or artefact? Sankhya B, 86(1):191–223, 2024
work page 2024
-
[21]
R.B. Davies and D.S. Harte. Tests for Hurst effect. Biometrika, 74(1):95–101, 1987
work page 1987
-
[22]
G. de Truchis, S. Fries, and A. Thomas. Forecasting extreme trajectories using seminorm representations. Preprint, 2025
work page 2025
-
[23]
I. Eliazar and J. Klafter. Fractal L´ evy correlation cascades.Journal of physics A: mathematical and theoretical, 40(16):F307, 2007
work page 2007
-
[24]
M. Garcin. Estimation of time-dependent Hurst exponents with variational smoothing and application to forecasting foreign exchange rates. Physica A: statistical mechanics and its applications, 483:462–479, 2017
work page 2017
-
[25]
M. Garcin. Hurst exponents and delampertized fractional Brownian motions. International journal of theoretical and applied finance , 22(05):1950024, 2019
work page 2019
-
[26]
M. Garcin. Fractal analysis of the multifractality of foreign exchange rates. Mathematical methods in economics and finance , 13-14(1):49–73, 2020
work page 2020
-
[27]
M. Garcin. A comparison of maximum likelihood and absolute moments for the estimation of Hurst exponents in a stationary framework. Communications in nonlinear science and numerical simulation, 114:106610, 2022
work page 2022
-
[28]
M. Garcin. Forecasting with fractional Brownian motion: a financial perspective. Quantitative finance, 22(8):1495–1512, 2022
work page 2022
-
[29]
M. Garcin and M. Grasselli. Long versus short time scales: the rough dilemma and beyond. Decisions in economics and finance , 45(1):257–278, 2022
work page 2022
-
[30]
J. Gatheral, T. Jaisson, and M. Rosenbaum. Volatility is rough. Quantitative finance , 18(6):933–949, 2018
work page 2018
-
[31]
D. Grahovac, N.N. Leonenko, and M.S. Taqqu. Scaling properties of the empirical struc- ture function of linear fractional stable motion and estimation of its parameters. Journal of statistical physics, 158:105–119, 2015
work page 2015
-
[32]
P. Guasoni, Y. Mishura, and M. R´ asonyi. High-frequency trading with fractional Brownian motion. Finance and stochastics, 25:277–310, 2021
work page 2021
-
[33]
P. Guasoni, Z. Nika, and M. R´ asonyi. Trading fractional Brownian motion.SIAM journal on financial mathematics, 10(3):769–789, 2019
work page 2019
-
[34]
C.D. Hardin. Skewed stable variables and processes. Technical Report 79, University of North Carolina, 1984
work page 1984
-
[35]
C.D. Hardin Jr, G. Samorodnitsky, and M.S. Taqqu. Nonlinear regression of stable random variables. Annals of applied probability, 1(4):582–612, 1991
work page 1991
- [36]
-
[37]
A. Janicki and A. Weron. Simulation and chaotic behavior of alpha-stable stochastic processes, volume 178. CRC Press, 1993
work page 1993
-
[38]
Y. Kasahara and M. Maejima. Weighted sums of iid random variables attracted to integrals of stable processes. Probability theory and related fields, 78(1):75–96, 1988
work page 1988
-
[39]
S.M. Kogon and D.B. Williams. Characteristic function based estimation of stable distribution parameters. In R. Adler, R. Feldman, and M. Taqqu, editors, A practical guide to heavy tails: statistical techniques and applications , pages 311–338. Springer, 1998
work page 1998
-
[40]
P.S. Kokoszka and M.S. Taqqu. Infinite variance stable ARMA processes. Journal of time series analysis, 15(2):203–220, 1994
work page 1994
-
[41]
I.A. Koutrouvelis. An iterative procedure for the estimation of the parameters of stable laws. Communications in statistics - simulation and computation , 10(1):17–28, 1981
work page 1981
-
[42]
P. Lambert and J.K. Lindsey. Analysing financial returns by using regression models based on non-symmetric stable distributions. Journal of the royal statistical society: series C (applied statistics), 48(3):409–424, 1999
work page 1999
-
[43]
K. Lamert, B.R. Auer, and R. Wunderlich. Discretization of continuous-time arbitrage strate- gies in financial markets with fractional Brownian motion.Mathematical methods of operations research, 101:163–218, 2025
work page 2025
-
[44]
Y. Lanoisel´ ee, G. Sikora, A. Grzesiek, D.S. Grebenkov, and A. Wy loma´ nska. Optimal pa- rameters for anomalous-diffusion-exponent estimation from noisy data. Physical review E , 98(6):062139, 2018
work page 2018
-
[45]
M.M. Ljungdahl and M. Podolskij. A minimal contrast estimator for the linear fractional stable motion. Statistical inference for stochastic processes, 23(2):381–413, 2020
work page 2020
-
[46]
B.B. Mandelbrot and J.W. van Ness. Fractional Brownian motions, fractional noises and applications. SIAM review, 10(4):422–437, 1968
work page 1968
- [47]
- [48]
-
[49]
G. Miller. Properties of certain symmetric stable distributions. Journal of multivariate anal- ysis, 8(3):346–360, 1978
work page 1978
-
[50]
J.P. Nolan. An algorithm for evaluating stable densities in Zolotarev’s (M) parameterization. Mathematical and computer modelling , 29(10-12):229–233, 1999
work page 1999
-
[51]
J.P. Nolan. Modeling financial data with stable distributions. In Handbook of heavy tailed distributions in finance, pages 105–130. North-Holland, 2003
work page 2003
-
[52]
J.P. Nolan. Truncated fractional moments of stable laws. Statistics & probability letters , 137:312–318, 2018
work page 2018
-
[53]
C.J. Nuzman and H.V. Poor. Linear estimation of self-similar processes via Lamperti’s trans- formation. Journal of applied probability , 37(2):429–452, 2000
work page 2000
-
[54]
V. Pipiras, M.S. Taqqu, and P. Abry. Can continuous-time stationary stable processes have discrete linear representations? Statistics & probability letters , 64(2):147–157, 2003. 24
work page 2003
-
[55]
V. Pipiras, M.S. Taqqu, and P. Abry. Bounds for the covariance of functions of infinite variance stable random variables with applications to central limit theorems and wavelet- based estimation. Bernoulli, 13(4):1091–1123, 2007
work page 2007
-
[56]
D. Rosadi and M. Deistler. Estimating the codifference function of linear time series models with infinite variance. Metrika, 73:395–429, 2011
work page 2011
-
[57]
D. Salas-Gonz´ alez, J.M. G´ orriz, J. Ram´ ırez, M. Schloegl, E.W. Lang, and A. Ortiz. Parame- terization of the distribution of white and grey matter in MRI using the α-stable distribution. Computers in biology and medicine , 43(5):559–567, 2013
work page 2013
-
[58]
D. Salas-Gonz´ alez, E.E. Kuruoglu, and D.P. Ruiz. Modelling with mixture of symmetric stable distributions using Gibbs sampling. Signal processing, 90(3):774–783, 2010
work page 2010
-
[59]
G. Samorodnitsky and M.S. Taqqu. Conditional moments and linear regression for stable random variables. Stochastic processes and their applications , 39(2):183–199, 1991
work page 1991
-
[60]
G. Samorodnitsky and M.S. Taqqu. Stable non-Gaussian random processes: stochastic models with infinite variance. Chapman & Hall, New York, London, 1994
work page 1994
-
[61]
M. ˇSapina, M. Garcin, K. Kramari´ c, K. Milas, D. Brdari´ c, and M. Piri´ c. The Hurst exponent of heart rate variability in neonatal stress, based on a mean-reverting fractional L´ evy stable motion. Fluctuation and noise letters , 19(03):2050026, 2020
work page 2020
-
[62]
V. Shergin. Estimating the Hurst exponent of fractional L´ evy motion by the fractional mo- ments method. In 2019 IEEE international scientific-practical conference problems of info- communications, science and technology, pages 719–722. IEEE, 2019
work page 2019
- [63]
-
[64]
S. Stoev and M.S. Taqqu. Simulation methods for linear fractional stable motion and FARIMA using the fast Fourier transform. Fractals, 12(01):95–121, 2004
work page 2004
-
[65]
S. Stoev and M.S. Taqqu. How rich is the class of multifractional Brownian motions? Stochas- tic processes and their applications , 116(2):200–221, 2006
work page 2006
-
[66]
D. Surgailis, G. Teyssi` ere, and M. Vaiˇ ciulis. The increment ratio statistic.Journal of multi- variate analysis, 99(3):510–541, 2008
work page 2008
-
[67]
M.S. Taqqu. Random processes with long-range dependence and high variability. Journal of geophysical research: atmospheres, 92(D8):9683–9686, 1987
work page 1987
-
[68]
L. Viitasaari. Representation of stationary and stationary increment processes via Langevin equation and self-similar processes. Statistics & probability letters , 115:45–53, 2016
work page 2016
- [69]
-
[70]
R. Weron. On the Chambers-Mallows-Stuck method for simulating skewed stable random variables. Statistics & probability letters , 28(2):165–171, 1996
work page 1996
-
[71]
W.A. Wilson. On semi-metric spaces. American journal of mathematics, 53(2):361–373, 1931
work page 1931
-
[72]
A. Wy loma´ nska, A. Chechkin, J. Gajda, and I.M. Sokolov. Codifference as a practical tool to measure interdependence. Physica A: statistical mechanics and its applications , 421:412–429, 2015
work page 2015
-
[73]
V.M. Zolotarev. One-dimensional stable distributions , volume 65. Translations of mathemat- ical monographs, AMS, 1986. 25 A Proof of Proposition 2 Proof. Using the independence of the Xi along with equation 1, we have, for any θ ∈ R, ΦPd i=1 aiXi(θ) = dY i=1 ΦXi(aiθ) = exp − dX i=1 ∥Xi∥α α|ai|α|θ|α ! , meaning thatPd i=1 aiXi is SαS with scale parameter ...
work page 1986
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.