REVIEW 2 major objections 4 minor 49 references
Drawdowns, Drawups, and Occupation Times under General Markov Models
T0 review · 2 major / 4 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read Five drawdown quantities become linear systems under any Markov model.
desk verdict Solid CTMC extension to five drawdown functionals, but the convergence theorem for repeated drawdowns assumes a path condition that fails for the diffusion models used in the numerics. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the first-passage resolvent of the CTMC, $P_S(k;f)=E[e^{-\int_0^{T_S}k(Y_s)\,ds}f(Y_{T_S})]$, which solves the linear system $(k-G)P_S=0$ and is available in closed form via (3). Every target quantity is written as a recursion of such resolvents by decomposing the drawdown time as $\tau_a=T^-_{x-a}$ on the event $\{\tau_a<T^+_x\}$, appending the running maximum or minimum as an extra state when the quantity depends on drawups or recovery, as in the $R$ and $S$ resolvents of (8) and (11). The recursions are solved backward from the upper absorbing state, and Sherman-Morrison-Woodbury updates for the inverse matrices yield the claimed complexity: $O(N^3)$ for general Markov models, $O(N)$ for diffusions for most quantities, and closed-form ratios for L\'evy models.
What would settle it
Run the CTMC scheme and a high-precision Monte Carlo simulation on a Markov process of the form (1) whose jumps can land exactly on the drawdown boundary, then compare the distribution of the second drawdown time with recovery as the mesh shrinks; if the limits disagree, the condition $P(X\in U\cap V\cap W)=1$ fails and the theorem's conclusion does not hold for that model.
Extended reading notes
Core claim
The central claim is that each of the five quantities satisfies an exact finite linear system once the Markov process $X$ is replaced by a CTMC $Y$: equation (7) for the drawdown time preceding the drawup time, (9) for the occupation time of the underlying until the drawdown time, (10) for the occupation time of the drawdown process until the drawdown time, (13) for the $n$-th drawdown time without recovery, and (16) for the $n$-th drawdown time with recovery. These systems are built from the first-passage resolvent of the chain, so the only approximation is the chain itself. Theorem 1 then states that the CTMC stopping times and occupation times converge jointly in distribution to those of the original process as the mesh goes to zero, under Assumption 1 and path-regularity conditions on the sets $U$, $V$, $W$, and $\widetilde{W}$. Numerical tables for Black-Scholes, CEV, double-exponential jump-diffusion, and variance-gamma models show extrapolated relative errors below one percent within seconds for digital options and drawdown insurance products.
Load-bearing premise
The convergence guarantee depends on Assumption 1 and on path-regularity conditions for the $n$-th drawdown times, $P(X\in U\cap\widetilde{W})=1$ and $P(X\in U\cap V\cap W)=1$, which the paper states but does not verify for the four models it tests numerically.
Editorial extensions
If this is right
- The five drawdown quantities can be computed for any Markov process of the form (1), removing the Brownian-motion or diffusion restrictions of earlier drawdown results.
- For the occupation-time quantities and the $n$-th drawdown functionals, the complexity matches path-independent pricing: $O(N^3)$ for general Markov models, $O(N)$ for diffusions, and $O(N^2)$ or $O(N^4)$ for the more path-dependent drawdown-before-drawup quantity.
- For L\'evy models, formulas (12), (15), and (18) turn several quantities into closed-form ratios, cutting runtime to under a second for some insurance and digital-option prices.
- The joint convergence in Theorem 1 means that Laplace-inverted derivative prices inherit the approximation: both the stopping time and the accumulated occupation time converge together.
Reading between the lines
- Going beyond the paper, the same recursion should directly implement the drawup occupation time until a drawdown and until an independent exponential time sketched in Remark 8, giving a natural stress test of the method on additional path-dependent functionals.
- A Monte Carlo check of the path-regularity conditions $P(X\in U\cap\widetilde{W})=1$ and $P(X\in U\cap V\cap W)=1$ for Black-Scholes, CEV, jump-diffusion, and variance-gamma parameters would turn the conditional convergence guarantee into an unconditional one for the models actually tested.
- Because the cost is linear in the number of CTMC states for diffusions, the same linear systems could be embedded in calibration or portfolio-optimization loops that evaluate drawdown quantities thousands of times, which the paper does not itself run.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper develops a continuous-time Markov chain (CTMC) approximation framework for computing five drawdown-related quantities under general one-dimensional Markov models: the drawdown time preceding the drawup time, generalized occupation times of the underlying process and of the drawdown process until drawdown, and the n-th drawdown times without and with recovery. For each quantity the authors derive linear systems satisfied under the CTMC and propose recursive algorithms with complexity O(N^3) for general Markov models and O(N) or O(N^2) for diffusions. Section 4 states a convergence theorem, Theorem 1, asserting distributional convergence of the CTMC stopping times and occupation times to their continuous counterparts as the mesh shrinks. Numerical experiments for Black-Scholes, CEV, double exponential jump-diffusion, and variance gamma models report first-order convergence and small errors.
Significance. The algorithmic contribution is substantial: explicit linear systems, efficient recursions, and complexity bounds for five nontrivial path-dependent quantities are valuable and largely self-contained. The numerical experiments are extensive and demonstrate practical accuracy. However, the central convergence guarantee for the two n-th drawdown quantities rests on Theorem 1(4)-(5), whose hypotheses are not satisfied by the diffusion and jump-diffusion models used in the corresponding numerical tables. This gap means the paper's main theoretical claim is currently established only for the first three quantities, not for the last two under the stated model classes.
major comments (2)
- [Section 4, definition of U and Theorem 1(4)-(5)] The set U requires that for every u≥0 the two hitting times inf{t≥u:ω_{u,t}-ω_t≥a} and inf{t≥u:ω_{u,t}-ω_t>a} coincide. For a continuous path that ever reaches drawdown a and subsequently downcrosses level a, take u to be a downcrossing time (the first return to a from above after the initial hit). At that u the drawdown equals a and immediately afterwards is strictly less than a, so the first time ≥a equals u while the first time >a is strictly larger; hence the path is not in U. Nondegenerate diffusions downcross level a infinitely often after the first hit, so for the Black-Scholes, CEV, and DEJD models used in Tables 4 and 5 we have P(X∈U)=0 rather than 1. Therefore Theorem 1(4) and (5) do not apply to these central examples, and the paper does not establish convergence of the CTMC approximations for the n-th drawdown quantities without and with recovery. The authors need to replace U by a condition that is actually satisfied by the intended model classes (for instance, a condition expressed in terms of quasi-left-continuity and the absence of exact drawdown equality at the relevant stopping times) and rework the proof accordingly.
- [Section 4, Theorem 1(4)-(5) and Appendix B.6] Even aside from the specific failure of U, the proof of Theorem 1(4)-(5) uses the membership of X in U to convert inequalities of the form '≥a' into '>a' in the limsup argument, and this step is essential for the claimed continuity of the n-th drawdown time mappings. Since U almost surely fails for continuous-path models, the proof cannot be patched by a minor rewording; the argument itself needs to be modified, for example by showing that the CTMC stopping times are asymptotically unaffected by the difference between weak and strict threshold crossing. Until such a proof is supplied, the convergence claims for the quantities in Sections 3.4 and 3.5 should be stated only conditionally on a verified path property, or the numerical convergence for the diffusion and jump-diffusion examples should be presented as empirical rather than as a consequence of Theorem 1.
minor comments (4)
- [Appendix B.1] In the proof of Proposition 1, the expression 'Y_{Y_x^+}' appears twice and is clearly a typo for the running maximum at the stopping time T_x^+; this makes the displayed derivation hard to follow.
- [Table 5] In the DEJD row with Nx=40, the reported absolute error is 0.1020, while the benchmark and CTMC values differ by 0.01020; this appears to be a factor-of-ten typographical error.
- [References] The reference 'Cherny and Ob/suppress l´oj' contains corrupted text and should read 'Cherny, V. and Oblój, J.'; the same corruption appears in the introduction.
- [Section 5] The benchmark values are stated to be obtained by wide grids and extrapolation, but the precise grid ranges and extrapolation procedure are not specified in the tables or text, which makes independent reproduction of the reported results more difficult.
Circularity Check
No significant circularity: the five linear systems are derived by first-step decompositions, the numerical values are solved from those exact systems with no fitted parameters, and the convergence proof rests on stated prior theorems rather than on the quantities being predicted.
full rationale
The paper's derivation chain is self-contained in the relevant sense: each of the five quantities is defined as an expectation under the CTMC approximation, and Propositions 1-5 derive exact linear systems (7), (9), (10), (13), and (16) by first-step (strong Markov) decompositions. The algorithms then solve these linear systems exactly; no parameter is calibrated to the target outputs, and no 'prediction' is a rename of an input. The convergence theorem is not circular: Theorem 1 assumes weak convergence of the CTMC approximation (from Mijatovic and Pistorius 2013) and invokes the prior drawdown-time continuity result of Zhang and Li (2023c) for the first drawdown time, but that prior result does not include the five occupation-time and nth-drawdown functionals proved here. The self-citations to Zhang and Li (2023c) are load-bearing in the sense that Lemma 1, Lemma 2, Assumption 1, and parts of Theorem 1 rely on that paper, but they are prior published mathematical results with explicitly stated assumptions and are used as building blocks, not as a way of assuming the present conclusions. The numerical 'benchmarks' are obtained from the same CTMC method on finer grids with extrapolation, so they are convergence checks rather than independent exact prices; this is a validation convention, not a fitted-input circularity. The unverified path-regularity hypotheses P(X in U cap ~W)=1 and P(X in U cap V cap W)=1 in Theorem 1(4)-(5) are assumption-support concerns and would affect correctness if false, but they are not a circular reduction of the theorem's conclusion to its inputs. Overall, the central derivation has independent mathematical content, so the circularity score is low.
Assumptions & free parameters
assumptions (4)
- domain assumption Assumption 1: X has no monotone sample paths, is quasi-left continuous, and its Levy measure satisfies stated conditions (absolute continuity or diffusion component).
- domain assumption P(X in U cap ~W)=1 and P(X in U cap V cap W)=1 for the n-th drawdown times without and with recovery.
- domain assumption There exists a sequence of CTMCs Y^(n) such that Y^(n) converges weakly to X as mesh goes to 0, with the CTMC generator G approximating the generator L in Appendix A.
- domain assumption The Abate-Whitt Fourier-series algorithm inverts the Laplace transforms accurately.
Cite this review
Pith. "Pith review of Drawdowns, Drawups, and Occupation Times under General Markov Models." pith.science (2026). https://pith.science/paper/ZSYZRSSX
@misc{pith2026250600552,
author = {Pith},
title = {Pith review of: Drawdowns, Drawups, and Occupation Times under General Markov Models},
year = {2026},
howpublished = {\url{https://pith.science/paper/ZSYZRSSX}},
note = {Machine review of arXiv:2506.00552}
}
read the original abstract
Drawdown risk, an important metric in financial risk management, poses significant computational challenges due to its highly path-dependent nature. This paper proposes a unified framework for computing five important drawdown quantities introduced in Landriault et al. (2015) and Zhang (2015) under general Markov models. We first establish linear systems and develop efficient algorithms for such problems under continuous-time Markov chains (CTMCs), and then establish their theoretical convergence to target quantities under general Markov models. Notably, the proposed algorithms for most quantities achieve the same complexity order as those for path-independent problems: cubic in the number of CTMC states for general Markov models and linear when applied to diffusion models. Rigorous convergence analysis is conducted under weak regularity conditions, and extensive numerical experiments validate the accuracy and efficiency of the proposed algorithms.
Figures
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Reference graph
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Reviewed August 7, 2026 · model on record in the stance chip above.
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