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[under "State-dependent splitting errors for anisotropic transport and diffusion: Source-verified counterexamples and an auxiliary estimate"]
# State-dependent splitting errors for anisotropic transport and diffusion: Source-verified counterexamples and an auxiliary estimate
[under "Abstract"]
We audit the source statements in arXiv:2603.08799v1, identified by a versioned PDF and its hash. An explicit smooth periodic shear contradicts the derivative-norm conservation assertion, which is also verified in the publisher's public Note 10. A positive-coefficient diffusion example exposes omitted mixed third derivatives in the preprint's displayed splitting prefactor. We quote the targeted preprint passages, distinguish a changed publisher note from the inaccessible publisher body, and make no claim that the unverified published diffusion formula is identical. For fixed trigonometric data we give the exact centered-stencil commutator and its order of convergence. Cosine-only numerical checks report initial and evolved-supremum comparators, finite-time limiting coefficients, and step refinement from pinned code. A standard auxiliary autonomous matrix estimate records the intermediate-state hypothesis needed for a corrected analysis; no novelty is claimed for that estimate. The results are specific counterexamples and proof obligations, not an exhaustive audit, an unconditional time-dependent PDE theorem, or a demonstrated quantum speedup.
[under "Scope, provenance, and standards of evidence"]
The audited object is the local nine-page PDF identifying itself as arXiv:2603.08799v1, submitted 9 March 2026 [1]. Its SHA-256 is `d03a710413b32ac622700adcfbaa9c3b8604ab9db00e45c348ea06c3d4be8988`. The source record links a published conference chapter [3]; we checked its public metadata, and its publicly exposed Notes, but could not obtain the full subscription chapter text. No finding here is asserted to apply unchanged to an unexamined revision, a later journal treatment, or other work by the same authors.
[under "An auxiliary conditional splitting estimate"]
## An auxiliary conditional splitting estimate
[under "An auxiliary conditional splitting estimate"]
State-dependent Trotter estimates are established tools. An, Fang, and Lin [2, Lemma 3, Theorem 4, Appendix B] give exact error representations and time-dependent unitary global bounds. Their first-order rate is $T^2/L$ and their second-order rate is $T^3/L^2$, with state factors controlled under structural relative-commutator assumptions. Their Lemma 7 handles partial exponential trajectories. We instead assume that difficult uniform control directly through $K$. We claim no novelty for the following auxiliary estimate.
[under "An auxiliary conditional splitting estimate"]
For constant controls, set $A=-iaH_1$, $B=-ibH_2$ in their unitary setting; the displayed defect integral below is the corresponding autonomous first-order representation. Contractive diffusion is not literally their unitary theorem, but the same standard defect/telescoping argument applies to contractive matrices. The explicit factor $1/2$ is the triangular integration area, not a new asymptotic result. Establishing a grid-independent $K$ for the audited stencil remains an unproved additional task.
[under "An auxiliary conditional splitting estimate"]
We deliberately state a finite-dimensional autonomous result. It does not extend silently to the source's time-dependent PDEs.
[under "Proposition 1: Auxiliary autonomous contraction estimate"]
#### Proposition 1: Auxiliary autonomous contraction estimate
[under "Reproducible checks and interpretation"]
The first deposited version used a sine field in its numerical table. This revision uses the analytic section's cosine field throughout; no equivalence of the complete sine and cosine evolutions is assumed. Appendix B supplies the exact fixed-mode stencil identity, the comparator formulas, the cosine results, and the order of limits. The original numerical files remain available as historical artifacts; the new revision script generates every new number.
[under "Limitations and open work"]
Independent human expert peer review has not been performed. Its strongest conclusions are the displayed identities, analytic counterexamples, and the conditional matrix theorem with a complete proof. The numerical checks supplement those arguments; they do not prove a quantum advantage or an unconditional PDE theorem. An exhaustive error claim would be unjustified.
[under "Appendix A: Source quotations and version-specific comparison"]
## Appendix A: Source quotations and version-specific comparison
[under "Appendix A: Source quotations and version-specific comparison"]
The supplied PDF is byte-identical to the publicly downloadable versioned arXiv object [1]: 200,554 bytes and SHA-256 d03a710413b32ac622700adcfbaa9c3b8604ab9db00e45c348ea06c3d4be8988. The following quotations and formulas were checked against its rendered pages. They are explicitly attributed to the preprint, not presumed to reproduce the complete Springer body.
[under "A.1 Own-coordinate restrictions, arXiv p. 2"]
### A.1 Own-coordinate restrictions, arXiv p. 2
[under "A.1 Own-coordinate restrictions, arXiv p. 2"]
> Additionally, we assume that the $c_j$ and the $\kappa_j$ functions are $2p+1$ differentiable, for some integer $p$, and do not depend on the $j$-th variables: $\forall j\in\{1,\ldots,d\}$, $\partial_{x_j}c_j=0$, $\partial_{x_j}\kappa_j=0$.
[under "A.1 Own-coordinate restrictions, arXiv p. 2"]
These hypotheses permit transverse variation. The examples in this note are smooth, periodic, and independent of the coefficients' own differentiation directions. The diffusion example has strictly positive coefficients and initial data of mean 1, so it also meets the later nonzero-mean requirement on arXiv p. 7.
[under "A.2 arXiv p. 5, footnote 8"]
### A.2 arXiv p. 5, footnote 8
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