REVIEW 2 major objections 4 minor 39 references
Hermite interpolation and data processing errors on Riemannian matrix manifolds
T0 review · 2 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read A single tangent-space curve solves Hermite interpolation on any Riemannian manifold carrying exponential and logarithm maps.
desk verdict Sound Hermite construction, but the 'error bounds' are asymptotic heuristics and the numerical comparison skips existing Hermite methods. 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 Riemannian normal-coordinate chart centered at the terminal point $q$: the interpolating curve is the exponential image of a cubic Hermite curve $\gamma(t)=a_0(t)\Delta_p+b_0(t)\hat v_p+b_1(t)\hat v_q$ in $T_qM$. The only non-elementary ingredient is the push-forward of the start velocity through the logarithm transition map, $\hat v_p=d(\operatorname{Log}_q)_p(v_p)$, which the paper evaluates by central differences as $\big((\operatorname{Log}_q\circ\operatorname{Exp}_p)(hv_p)-(\operatorname{Log}_q\circ\operatorname{Exp}_p)(-hv_p)\big)/(2h)$; for the Stiefel manifold the paper derives an explicit formula for the derivative of the exponential via a block-matrix identity for the derivative of the matrix exponential. The curvature error bound is carried by the Jacobi-field expansion of $d(\operatorname{Exp}_q)_{\delta w}(\delta w^\perp)$, which is exactly the mechanism that turns tangent-space errors into manifold distances.
What would settle it
On a sphere, choose two tangent vectors $\Delta,\tilde\Delta$ at a point $q$ with small angle $s_0$ and norms $\delta,\tilde\delta<1$, compute the endpoints via the exponential map, and measure their geodesic distance; the inequality (3.1) predicts a specific shortening relative to the flat tangent-space distance, so a measured lengthening beyond the $O(s_0^2)$ term would refute the curvature relation.
Extended reading notes
Core claim
The central discovery is that a curve of the form $$c(t)=\operatorname{Exp}_q\big(a_0(t)\Delta_p+b_0(t)\hat v_p+b_1(t)\hat v_q\big)$$ with $\Delta_p=\operatorname{Log}_q(p)$, $\hat v_p=d(\operatorname{Log}_q)_p(v_p)$, and $\hat v_q=v_q$ solves the Hermite interpolation problem $c(t_0)=p$, $c(t_1)=q$, $\dot c(t_0)=v_p$, $\dot c(t_1)=v_q$ on any Riemannian manifold, provided $p$ and $q$ are not conjugate and the logarithm is defined. The proof works by expressing the whole curve in normal coordinates centered at the endpoint $q$, where the endpoint condition is automatic and the start condition becomes a single application of the differential of the logarithm. A second result relates the manifold distance between two exponential images of nearby tangent vectors to their tangent-space distance, with a first-order correction $\delta s_0\big(1-\tfrac{K_q(\sigma)}6\delta^2+o(\delta^2)\big)$ determined by the sectional curvature $K_q(\sigma)$: positive curvature shortens the propagated error, negative curvature amplifies it.
Load-bearing premise
The whole construction depends on consecutive sample points being close enough on the curved space that the map pulling one point back to the other's tangent space exists and that a small-step numerical derivative of that map is accurate.
Editorial extensions
If this is right
- The method transfers to any Riemannian manifold with computable exponential and logarithm maps, including manifolds that carry no Lie-group, homogeneous-space, or symmetric-space structure.
- Composite interpolation over many sample points is globally $C^1$ by construction, because each local arc ends with exactly the velocity that the next arc starts with.
- Constructing the full curve costs $3k$ logarithm and $2k$ exponential evaluations for $k$ intervals, and each evaluation of the final curve costs one exponential evaluation, which is below the cost of the composite Bezier alternatives the paper compares against.
- The same normal-coordinate machinery derives explicit manifold error bounds for any data-processing scheme that maps data to a tangent space, processes it there, and maps back to the manifold.
- On the Stiefel manifold, the method interpolates the factors of QR and SVD decompositions with smaller relative Frobenius errors than geodesic or tangent-space RBF interpolation in the reported experiments.
Reading between the lines
- Because the local curve is anchored in normal coordinates at the right endpoint, swapping the endpoints changes the interpolant; an adaptive choice of anchor, for instance the endpoint with the larger remaining step, could reduce the chance that the logarithm fails, an effect the paper only observes numerically.
- The curvature bound suggests an operational rule not stated by the author: on manifolds of positive sectional curvature, small tangent-space processing errors shrink on the manifold, so cheaper approximations such as retractions in place of exponentials may be safe; this could be tested by repeating the Stiefel experiments with retraction-based derivative transport.
- The same transition-map derivative can in principle be computed to any order in the step size $h$ by higher-order finite differences or by differentiating the logarithm algorithm itself, which would remove the $O(h^2)$ error in the endpoint velocity without changing the interpolation formula.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a Riemannian generalization of local cubic Hermite interpolation. Given two sample points p, q and tangent vectors v_p, v_q on a Riemannian manifold, the method maps the data into the tangent space T_qM via the Riemannian logarithm, constructs the ordinary Euclidean cubic Hermite polynomial in that tangent space using the basis functions a0, b0, b1, and maps the result back to the manifold via the exponential map. The endpoint velocity at q is automatic, while the velocity at p is matched by transporting v_p through the differential d(Log_q)_p. The paper proves this construction in Theorem 2.1, discusses the practical finite-difference approximation of d(Log_q)_p, compares the computational effort with Bézier-type methods, and then derives an asymptotic relation between data-processing errors in normal coordinates and the sectional curvature of the manifold (Theorem 3.1). The numerical part specializes the framework to the compact Stiefel manifold, including formulas for differentiating the Stiefel exponential via Mathias' theorem, and presents experiments for the QR decomposition, low-rank SVD interpolation, and a Black-Scholes option-pricing application.
Significance. The Hermite construction is elementary, geometrically natural, and potentially useful: it applies to any Riemannian manifold for which exp and log algorithms are available, and the explicit Stiefel derivative formula in Lemma 4.1 is a concrete computational contribution. The numerical experiments are relevant and cover nontrivial applications. The paper also openly identifies its main practical constraint, namely that consecutive samples must lie close enough for the Stiefel logarithm to converge. The curvature-error relation in Theorem 3.1 is conceptually attractive and gives a clean qualitative explanation of why the manifold errors in the Stiefel experiments are slightly smaller than the tangent-space errors. However, as written the theorem is an asymptotic expansion, not a computable error bound; this is the main gap between the abstract's claims and the actual result. The central Hermite derivation is sound, and the overclaim is local and fixable, so the appropriate outcome is a major revision rather than rejection.
major comments (2)
- [Abstract; Theorem 3.1, Eq. (3.1)] The abstract states that the paper 'provides general error bounds for manifold data processing methods', but Theorem 3.1 is an asymptotic estimate rather than a bound in the usual numerical-analysis sense. The right-hand side of Eq. (3.1) contains the unquantified terms o(δ^2) and O(s0^2), and the hypotheses δ, δ~<1 do not by themselves control these remainders; no explicit smallness condition involving the curvature or the injectivity radius is given. Consequently, for a fixed manifold with large sectional curvature, the displayed inequality cannot be evaluated or certified as a worst-case bound. Section 5.3 uses only the sign of the Stiefel curvature, not the quantitative content of the theorem. I recommend replacing 'general error bounds' by 'asymptotic error estimates' throughout, or alternatively adding explicit constants and a sufficient smallness condition under which the estimate is a true inequality with a computable remainder.
- [Section 2.2, Eq. (2.11); Section 5.1] Theorem 2.1 is proved for the exact choice v_hat_p = d(Log_q)_p(v_p), but the general implementation described in Section 2.2 replaces this differential by the central finite-difference approximation in Eq. (2.11). The paper does not provide an error analysis showing how the O(h^2) truncation error and the convergence threshold of the iterative Stiefel logarithm affect the satisfaction of the Hermite conditions (1.2) or the C^1 assembly in Remark 1. The table in Section 5.1 gives empirical reconstruction errors for h = 10^-2 through 10^-7, but no theoretical statement links h to the interpolation error. Since the claimed generality is 'only exp and log algorithms are needed', the manuscript should either include a clear statement that the implemented curve satisfies the Hermite conditions only up to O(h^2) plus solver tolerance, or provide an explicit error estimate for the finite-difference step.
minor comments (4)
- [Section 5.2 and Section 5.3] The figure numbering is inconsistent: the error curves in Section 5.2 are first introduced as Fig. 5.1 and then referenced as Fig. 5.2, and Section 5.3 again labels a plot as Fig. 5.2. Please renumber the figures and check all cross-references.
- [Section 5.4] The section title refers to 'left singular values', but the experiment interpolates the left singular vectors U(μ); please adjust the title or the wording.
- [Theorem 3.1] The notation σ = span(Δ, Δ~) assumes that Δ and Δ~ span a two-plane; when the two vectors are collinear, the sectional curvature K_q(σ) is not defined. Please add a convention for the collinear case or handle s0 = 0 separately.
- [Remark 2(i)] The relation ε ≥ δ‖w(0)-w(s0)‖ and the subsequent bound δs0 ≤ 2δ arcsin(ε/(2δ)) are used to pass to Eq. (3.5), but Eq. (3.5) is only an asymptotic replacement for the exact angle-dependent expression; please state explicitly that the equality there is valid up to O(ε^2).
Circularity Check
No circularity: the Hermite construction is an explicit existence proof and the curvature estimate is a standard Jacobi-field expansion, not a fit.
full rationale
The central derivation (Theorem 2.1) constructs the interpolant explicitly: the auxiliary vector is defined by the inverse-function identity vhat_p = d(Log_q)_p(v_p), and the endpoint derivative then satisfies d(Exp_q)_{Delta_p}(vhat_p) = v_p because d(Log_q)_p is the inverse of d(Exp_q)_{Delta_p}. This is an existence/construction argument, not a fitted or renamed input. The curvature estimate (Theorem 3.1) is a Taylor expansion of the transition map Log_p o Exp_q along a circular arc, using the standard Jacobi-field estimate from do Carmo; it contains no fitted constants and is not derived from the Hermite ansatz. The paper's self-citations ([37] Stiefel logarithm, [38] manifold interpolation background) are used as computational tools and comparison baselines: [37] is an algorithm reproduced in Appendix D with stated assumptions, and the proof of Theorem 2.1 and Theorem 3.1 does not depend on it. The only notable caveat is a rigor/limitation issue, not circularity: Theorem 3.1 is an asymptotic expansion with o(delta^2) and O(s0^2) remainders, so the abstract's phrase 'general error bounds' overstates what is proved, and the conclusions admit that the main practical constraint is that consecutive samples must be close enough for the Stiefel logarithm to be well-defined. These are correctness and applicability observations, and they do not make the derivation circular.
Assumptions & free parameters
free parameters (1)
- finite difference step h =
1e-4
assumptions (7)
- standard math d(Exp_p)_0 = id, i.e., the exponential map differential at the origin is the identity.
- domain assumption The sample points p and q are not conjugate along the connecting geodesic.
- standard math Jacobi field asymptotic: ||J(t)|| = t - (K/6)t^3 + o(t^3) along a unit-speed geodesic.
- domain assumption All data lies within the injectivity radius of the center q.
- domain assumption The Stiefel exponential is given by the formula (4.2) with the canonical metric.
- domain assumption Stiefel sectional curvature is bounded by 0 ≤ K ≤ 5/4.
- domain assumption The QR decomposition and SVD of the sampled matrix curves are differentiable.
Cite this review
Pith. "Pith review of Hermite interpolation and data processing errors on Riemannian matrix manifolds." pith.science (2026). https://pith.science/paper/IE6FMOMQ
@misc{pith2026190805875,
author = {Pith},
title = {Pith review of: Hermite interpolation and data processing errors on Riemannian matrix manifolds},
year = {2026},
howpublished = {\url{https://pith.science/paper/IE6FMOMQ}},
note = {Machine review of arXiv:1908.05875}
}
read the original abstract
The main contribution of this paper is twofold: On the one hand, a general framework for performing Hermite interpolation on Riemannian manifolds is presented. The method is applicable, if algorithms for the associated Riemannian exponential and logarithm mappings are available. This includes many of the matrix manifolds that arise in practical Riemannian computing application such as data analysis and signal processing, computer vision and image processing, structured matrix optimization problems and model reduction. On the other hand, we expose a natural relation between data processing errors and the sectional curvature of the manifold in question. This provides general error bounds for manifold data processing methods that rely on Riemannian normal coordinates. Numerical experiments are conducted for the compact Stiefel manifold of rectangular column-orthogonal matrices. As use cases, we compute Hermite interpolation curves for orthogonal matrix factorizations such as the singular value decomposition and the QR-decomposition.
Figures
Figures from the paper (7 more)
Reference graph
Works this paper leans on
-
[1]
P.-A. Absil, P.-Y. Gousenbourger, P. Striewski, and B. Wirth. Differentiable piecewise-B´ ezier surfaces on Riemannian manifolds. SIAM Journal on Imaging Sciences , 9(4):1788–1828, 2016. 25 Algorithm 4 Stiefel logarithm Input: base point U∈St(n,p ) and ˜U∈St(n,p ) ‘close’ to base point, τ >0 conver- gence threshold 1: M :=UT ˜U∈ Rp×p 2: QN := ˜U−UM∈ Rn×p #...
work page 2016
- [2]
-
[3]
D. Alekseevsky, A. Kriegl, P. W. Michor, and M. Losik. Choosing roots of polynomials smoothly. Israel Journal of Mathematics , 105(1):203–233, 1998
work page 1998
- [4]
-
[5]
D. Amsallem and C. Farhat. Interpolation method for adapting reduced-order models and application to aeroelasticity. AIAA Journal, 46(7):1803–1813, 2008
work page 2008
-
[6]
R.H. Bartels, J.C. Beatty, and B.A. Barsky. An Introduction to Splines for Use in Computer Graphics and Geometric Modeling . Morgan Kaufmann Series in Comp. Elsevier Science, 1995
work page 1995
-
[7]
R. Bhatia. Matrix Analysis. Number 169 in Graduate Texts in Mathematics. Springer-Verlag, New York – Berlin – Heidelberg, 1997
work page 1997
-
[8]
F. Black and M. Scholes. The pricing of options and corporate liabilities. J. Polit. Econ. , 81(3):637–654, 1973
work page 1973
Show all 39 references
-
[9]
Boumal and P.-A
N. Boumal and P.-A. Absil. A discrete regression method on manifolds and its application to data on SO(n). IFAC Proceedings Volumes, 44(1):2284 – 2289, 2011. 18th IFAC World Congress
2011
-
[10]
Bunse-Gerstner, R
A. Bunse-Gerstner, R. Byers, V. Mehrmann, and N. K. Nichols. Numerical computation of an analytic singular value decomposition of a matrix valued function.Numerische Mathematik, 60(1):1–39, 1991
1991
-
[11]
Camarinha, F
M. Camarinha, F. Silva Leite, and P. Crouch. On the geometry of riemannian cubic polynomials. Differential Geometry and its Applications , 15(2):107 – 135, 2001
2001
-
[12]
Crouch and F
P. Crouch and F. Silva Leite. The dynamic interpolation problem: On Riemannian manifolds, Lie groups, and symmetric spaces. Journal of Dynamical and Control Systems , 1(2):177– 202, 1995
1995
-
[13]
M. P. do Carmo. Riemannian Geometry. Mathematics: Theory & Applications. Birkh¨ auser Boston, 1992
1992
-
[14]
Edelman, T
A. Edelman, T. A. Arias, and S. T. Smith. The geometry of algorithms with orthogonality constraints. SIAM Journal on Matrix Analysis and Applications , 20(2):303–353, April 1998
1998
-
[15]
Oliphant, P
E.Jones, T. Oliphant, P. Peterson, et al. SciPy: Open source scientific tools for Python, 2001–. [Online; accessed July 2019
2001
-
[16]
Gousenbourger, E
P.-Y. Gousenbourger, E. Massart, and P.-A. Absil. Data fitting on manifolds with composite 26 B´ ezier-like curves and blended cubic splines.Journal of Mathematical Imaging and Vision , online:1–27, 2018
2018
-
[17]
B. C. Hall. Lie Groups, Lie Algebras, and representations: An elementary introduction . Springer Graduate texts in Mathematics. Springer–Verlag, New York – Berlin – Heidel- berg, 2nd edition, 2015
2015
-
[18]
A. Hay, J. T. Borggaard, and D. Pelletier. Local improvements to reduced-order models using sensitivity analysis of the proper orthogonal decomposition. Journal of Fluid Mechanics , 629:41–72, 2009
2009
-
[19]
N. J. Higham. Functions of Matrices: Theory and Computation . Society for Industrial and Applied Mathematics, Philadelphia, PA, USA, 2008
2008
-
[20]
Hohmann and P
A. Hohmann and P. Deuflhard. Numerical Analysis in Modern Scientific Computing: An Introduction. Texts in Applied Mathematics. Springer New York, 2003
2003
-
[21]
Jakubiak, F
J. Jakubiak, F. S. Leite, and R. Rodrigues. A two-step algorithm of smooth spline generation on riemannian manifolds. Journal of Computational and Applied Mathematics , 194:177–191, 2006
2006
-
[22]
H.Le K. R. Kim, I. L. Dryden. Smoothing splines on riemannian manifolds, with applications to 3D shape space. arXiv:1801.04978v2, 2018
2018 arXiv
-
[23]
K. A. Krakowski, L. Machado, F. Silva Leite, and J. Batista. Solving interpolation prob- lems on Stiefel manifolds using quasi-geodesics. In Pr´ e-Publica¸ ci˜ oes do Departamento de Matem´ atica, number 15–36, Universidade de Coimbra, 2015
2015
-
[24]
J. M. Lee. Riemannian Manifolds: an Introduction to Curvature . Springer Verlag, New York – Berlin – Heidelberg, 1997
1997
-
[25]
J. M. Lee. Introduction to Smooth Manifolds . Graduate Texts in Mathematics. Springer New York, 2012
2012
-
[26]
Narcowich
F. Narcowich. Generalized Hermite interpolation and positive definite kernels on a Riemannian manifold. Journal of Mathematical Analysis and Applications , 190:165–193, 1995
1995
-
[27]
Nava-Yazdani and K
E. Nava-Yazdani and K. Polthier. De Casteljau’s algorithm on manifolds. Computer Aided Geometric Design, 30(7):722–732, 2013
2013
-
[28]
Noakes, G
L. Noakes, G. Heinzinger, and B. Paden. Cubic splines on curved spaces. IMA Journal of Mathematical Control and Information , 6(4):465–473, 12 1989
1989
-
[29]
Popiel and L
T. Popiel and L. Noakes. B´ ezier curves and C2 interpolation in Riemannian manifolds.Journal of Approximation Theory, 148(2):111–127, 2007
2007
-
[30]
Rentmeesters
Q. Rentmeesters. Algorithms for data fitting on some common homogeneous spaces . PhD thesis, Universit´ e Catholique de Louvain, Louvain, Belgium, 2013
2013
-
[31]
Samir, P.-A
C. Samir, P.-A. Absil, A. Srivastava, and E. Klassen. A gradient-descent method for curve fitting on Riemannian manifolds. Foundations of Computational Mathematics , 12(1):49– 73, Feb 2012
2012
-
[32]
Samir and I
C. Samir and I. Adouani. C1 interpolating B´ ezier path on Riemannian manifolds, with appli- cations to 3D shape space. Applied Mathematics and Computation , 348:371 – 384, 2019
2019
-
[33]
Steinke, M
F. Steinke, M. Hein, J. Peters, and B. Schoelkopf. Manifold-valued Thin-Plate Splines with Applications in Computer Graphics. Computer Graphics Forum, 2008
2008
-
[34]
S. F. Walter, L. Lehmann, and R. Lamour. On evaluating higher-order derivatives of the QR decomposition of tall matrices with full column rank in forward and reverse mode algorithmic differentiation. Optimization Methods and Software , 27(2):391–403, 2012
2012
-
[35]
Wen and W
Z. Wen and W. Yin. A feasible method for optimization with orthogonality constraints. Math- ematical Programming, 142(1):397–434, Dec 2013
2013
-
[36]
Zimmermann
R. Zimmermann. On the maximum likelihood training of gradient-enhanced spatial Gaussian processes. SIAM Journal on Scientific Computing , 35(6):A2554–A2574, 2013
2013
-
[37]
Zimmermann
R. Zimmermann. A matrix-algebraic algorithm for the Riemannian logarithm on the Stiefel manifold under the canonical metric. SIAM Journal on Matrix Analysis and Applications , 38(2):322–342, 2017
2017
-
[38]
Zimmermann
R. Zimmermann. Manifold interpolation and model reduction. arXiv:1902.06502v1, 2019
1902 arXiv
-
[39]
Zimmermann and K
R. Zimmermann and K. Debrabant. Parametric model reduction via interpolating orthonormal bases. In F. A. Radu, K. Kumar, I. Berre, D. N. Nordbotten, and I. S. Pop, editors, Nu- merical Mathematics and Advanced Applications ENUMATH 2017. Springer International Publishing, Cham,...
2017
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