arXiv research

Solves initial value problem for harmonic maps on specific manifolds.

We consider a regular singular Sturm-Liouville operator $L:=-\frac{d^2}{dx^2} + \frac{q(x)}{x^2 (1-x)^2}$ on the line segment $[0,1]$. We impose certain boundary conditions such that we obtain a semi-bounded self-adjoint operator. It is known that the $ζ$-function of this operator $ζ_L(s)=\sum_{λ\in\spec(L)\setminus\{0…

Bootstrapping regularizes singular correlation matrices, reducing the need for complex regularization.

Singular value decomposition (SVD) is the mathematical basis of principal component analysis (PCA). Together, SVD and PCA are one of the most widely used mathematical formalism/decomposition in machine learning, data mining, pattern recognition, artificial intelligence, computer vision, signal processing, etc. In recen…

We give a new proof for the local existence of a smooth isometric embedding of a smooth $3$-dimensional Riemannian manifold with nonzero Riemannian curvature tensor into $6$-dimensional Euclidean space. Our proof avoids the sophisticated arguments via microlocal analysis used in earlier proofs. In Part 1, we introduce …

Stability of branched immersions with energy constraints.

In this article the degenerate warped products of singular semi-Riemannian manifolds are studied. They were used recently by the author to handle singularities occurring in General Relativity, in black holes and at the big-bang. One main result presented here is that a degenerate warped product of semi-regular semi-Rie…

Study of defects in gauge theories connects quantum field theory to classical integrability.

Researchers determine all possible representations of monodromy for Schwarzian equations on punctured surfaces.

In this paper, we study the structure of the pointed-Gromov-Hausdorff limits of sequences of Ricci shrinkers. We define a regular-singular decomposition following the work of Cheeger-Colding for manifolds with a uniform Ricci curvature lower bound, and prove that the regular part of any Ricci shrinker limit space is co…

The generalized Weierstrass representation is used to analyze the asymptotic behavior of a constant mean curvature surface that arises locally from an ordinary differential equation with a regular singularity. We prove that a holomorphic perturbation of an ODE that represents a Delaunay surface generates a constant mea…

This paper considers nonlinear regular-singular stochastic optimal control of large insurance company. The company controls the reinsurance rate and dividend payout process to maximize the expected present value of the dividend pay-outs until the time of bankruptcy. However, if the optimal dividend barrier is too low t…

We generalize the classical Beauville-Narasimhan-Ramanan correspondence to the case of parabolic Higgs bundles with regular singularities and Higgs $V$-bundles. Using this correspondence along with Bott-Morse theoretic techniques we provide an exact component count for moduli spaces of maximal parabolic $\text{Sp}\left…

We study tt*-geometry on the classifying space for regular singular TERP-structures, e.g., Fourier-Laplace transformations of Brieskorn lattices of isolated hypersurface singularities. We show that (a part of) this classifying space can be canonically equipped with a hermitian structure. We derive an estimate for the h…

We investigate variations of Brieskorn lattices over non-compact parameter spaces, and discuss the corresponding limit objects on the boundary divisor. We study the associated variation of twistors and the corresponding limit mixed twistor structures. We construct a compact classifying space for regular singular Briesk…

We compared the regular Singular Value Decomposition (SVD), truncated SVD, Krylov method and Randomized PCA, in terms of time and space complexity. It is well-known that Krylov method and Randomized PCA only performs well when k << n, i.e. the number of eigenpair needed is far less than that of matrix size. We compared…

The paper defines function spaces on manifolds with bounded or singular geometries.

Proves an ε-regularity theorem for Ricci flows, leading to new singularity estimates.

Proves regularity of harmonic maps into Teichmüller space.

Let (E,D,P) be a flat vector bundle with a parabolic structure over a punctured Riemann surface, (M,g). We consider a deformation of the harmonic metric equation which we call the Poisson metric equation. This equation arises naturally as the dimension reduction of the Hermitian-Yang-Mills equation for holomorphic vect…

Examples of area-minimizing graphs with low regularity in a specific group.

We present authors' new theory of the RT-equations, nonlinear elliptic partial differential equations which determine the coordinate transformations which smooth connections $Γ$ to optimal regularity, one derivative smoother than the Riemann curvature tensor ${\rm Riem}(Γ)$. As one application we extend Uhlenbeck compa…

A sequence of rational functions in a variable $q$ is $q$-holonomic if it satisfies a linear recursion with coefficients polynomials in $q$ and $q^n$. We prove that the degree of a $q$-holonomic sequence is eventually a quadratic quasi-polynomial. Our proof uses differential Galois theory (adapting proofs regarding hol…

Symmetry reduction of Painlevé IV to Flaschka-Newell Painlevé II

This paper explores how local behavior of meromorphic connections on the projective line determines the global connection.

The article extends Thurston's Grafting Theorem to signed spaces and defines a framed monodromy map.

Given a rank-two sub-Riemannian structure $(M,Δ)$ and a point $x_0\in M$, a singular curve is a critical point of the endpoint map $F:γ\mapstoγ(1)$ defined on the space of horizontal curves starting at $x_0$. The typical least degenerate singular curves of these structures are called \emph{regular singular curves}; the…

Based on a point of view that solvency and security are first, this paper considers regular-singular stochastic optimal control problem of a large insurance company facing positive transaction cost asked by reinsurer under solvency constraint. The company controls proportional reinsurance and dividend pay-out policy to…

Stochastic gradient descent regularizes least squares problems by smoothing large singular values.

Solves Deligne-Simpson problem for special connections on Gm.

Study cohomogeneity one solitons for $G_2$-structures on various manifolds.

Let $E$ be a vector bundle over a suitable differential manifold $M$ and let $\wedge^p E$ denote $p$-exterior product of $E$. Given sections $ω_1,\dots,ω_k$ of $E$ and a section $η$ of $\wedge^p E$, we consider the problem if $η$ can be written in the form $η=\sum ω_i\wedgeγ_i,$ where $γ_i$ are sections of $\wedge^{p…

Study optimal consumption with relaxed benchmarks and drawdown constraints.

On a Riemannian or a semi-Riemannian manifold, the metric determines invariants like the Levi-Civita connection and the Riemann curvature. If the metric becomes degenerate (as in singular semi-Riemannian geometry), these constructions no longer work, because they are based on the inverse of the metric, and on related o…

We prove that the essential smoothness of the gravitational metric at shock waves in GR, a PDE regularity issue for weak solutions of the Einstein equations, is determined by a geometrical condition which we introduce and name the {\it Riemann-flat condition}. The Riemann-flat condition determines whether or not the es…

New algorithm for Coxeter connections with maximally ramified singularities.

Extends optimal regularity and Uhlenbeck compactness to non-Riemannian manifolds.

Paper proposes a graph network for EHR data that learns robust representations.

Overview of integrable systems with symmetries, focusing on toric and semitoric systems.

New method to derive integrable systems from existing Lax systems.

Learning to control linear systems is statistically hard, especially for underactuated systems.

Discrete-time systems can be characterized by simple flat coordinates and their shifts.

The paper explores when linear system identification is hard or easy, especially for under-actuated systems.

This paper improves system identification by reducing sample complexity for high-dimensional linear dynamical systems.

In integrable hydrodynamic systems, coordinates exist where generators and symmetries are simple.

This paper studies nonholonomic constraints in Hamiltonian systems, deriving equations and theorems.

New method models unknown systems with hidden parameters using neural networks.

Study absolute equivalence for Pfaffian systems, applying to control systems.