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Jingwei Chen

Publications and source records attributed to Jingwei Chen.

At least 19 recordsLinked to original sources

Stochastic maximum principle for time-changed forward-backward stochastic control problem with L\'evy noise

This paper establishes a stochastic maximum principle for optimal control problems governed by time-changed forward-backward stochastic differential equations with L\'evy noise. The system incorporates a random, non-decreasing operational time (the inverse of an $\alpha$-stable subordinator) to model phenomena like trapping events and subdiffusion. Using a duality transformation and the convex variational method, we derive necessary and sufficient conditions for optimality, expressed through a novel set of adjoint equations. Finally, the theoretical results are applied to solve an explicit cash management problem under stochastic recursive utility.

math.OC

Entropy-Reservoir Bregman Projection: An Information-Geometric Unification of Model Collapse

Self-referential learning -- training a model on data it generated itself -- promises boundless scalability but chronically suffers from model collapse: language models degenerate into repetitive text, GANs drop modes, and reinforcement-learning policies over-exploit. Although practitioners employ ad~hoc fixes such as real-data mixing, entropy bonuses, knowledge distillation, or retrieval-augmented generation, a single principle that explains both the failure mode and the success of these fixes has remained elusive. We present Entropy-Reservoir Bregman Projection (ERBP), an information-geometric framework that unifies these phenomena. We model the closed loop as a stochastic Bregman projection sequence in distribution space. Without external coupling, finite-sample noise forces the system to project onto an ever-shrinking empirical support, causing exponential entropy decay and eventual collapse. Introducing an Entropy Reservoir -- a high-entropy distribution mixed into each projection -- injects a controllable entropy flux that provably stabilises the dynamics. Our theory yields (i) a necessary condition for collapse, (ii) a sufficient condition that guarantees a non-trivial entropy floor, and (iii) closed-form rates that depend only on sample size and the strong-convexity/Lipschitz constants of the Bregman generator. Experiments on large-language-model self-training, Soft Actor-Critic in reinforcement learning, and GAN optimisation validate our predictions and show that disparate stabilisation heuristics correspond to specific reservoir choices and coupling coefficients. ERBP thus transforms a collection of folk remedies into a single, quantitative design rule: monitor and budget your entropy flux.

cs.LG

$\alpha$-scaled strong convergence of stochastic theta method for stochastic differential equations driven by time-changed L\'evy noise beyond Lipschitz continuity

This paper develops an $\alpha$-parametrized framework for analyzing the strong convergence of the stochastic theta (ST) method for stochastic differential equations driven by time-changed L\'evy noise (TCSDEwLNs) with time-space-dependent coefficients satisfying local Lipschitz conditions. Properties of the inverse subordinator are investigated and explicit moment bounds for the exact solution are derived with jump rate incorporated. The analysis demonstrates that the ST method converges strongly with order of $min\{\eta_{F},\eta_{G},\eta_{H},\alpha/2\}$, establishing a precise relationship between numerical accuracy and the time-change mechanism. This theoretical advancement extends existing results and would facilitate applications in finance and biology where time-changed L\'evy models are prevalent.

math.PR

Strong convergence and Mittag-Leffler stability of stochastic theta method for time-changed stochastic differential equations

We propose the first $\alpha$-parameterized framework for solving time-changed stochastic differential equations (TCSDEs), explicitly linking convergence rates to the driving parameter of the underlying stochastic processes. Theoretically, we derive exact moment estimates and exponential moment estimates of inverse $\alpha$-stable subordinator $E$ using Mittag-Leffler functions. The stochastic theta (ST) method is investigated for a class of SDEs driven by a time-changed Brownian motion, whose coefficients are time-space-dependent and satisfy the local Lipschitz condition. We prove that the convergence order dynamically responds to the stability index $\alpha$ of stable subordinator $D$, filling a gap in traditional methods that treat these factors independently. We also introduce the notion of Mittag-Leffler stability for TCSDEs, and investigate the criterion of Mittag-Leffler stability for both the exact and numerical solutions. Finally, some numerical simulations are presented to illustrate the theoretical results.

math.PR

On the probability of generating a primitive matrix

Given a $k\times n$ integer primitive matrix $\bf{A}$ (i.e., a matrix can be extended to an $n\times n$ unimodular matrix over the integers) with the maximal absolute value of entries $\|\bf{A}\|$ bounded by {an integer} $λ$ from above, we study the probability that the $m\times n$ matrix extended from $\bf{A}$ by appending other $m-k$ row vectors of dimension $n$ with entries chosen randomly and independently from the uniform distribution over $\{0, 1,\ldots, λ-1\}$ is still primitive. We present a complete and rigorous proof of a lower bound on the probability, which is at least a constant for fixed $m$ in the range $[k+1, n-4]$. As an application, we prove that there exists a fast Las Vegas algorithm that completes a $k\times n$ primitive matrix $\bf{A}$ to an $n\times n$ unimodular matrix within expected $\tilde{O}(n^ω\log \|\bf{A}\|)$ bit operations, where $\tilde{O}$ is big-$O$ but without log factors, $ω$ is the exponent on the arithmetic operations of matrix multiplication.

cs.SC

A numerical study of the effect of discretization methods on the crystal plasticity finite element method

The present report describes a big data numerical study of crystal plasticity finite element (CPFE) modelling using static and grain-based meshing to investigate the dependence of the results on the discretization approach. Static mesh refers to the integration point-based representation of the microstructure in which the integration points (IPs) within a finite element may belong to different grains, while in the grain-based meshing the minimum discretization unit is an element that may only belong to one grain. The crystal plasticity constitutive law was coded using UMAT subroutine within commercial finite element software Abaqus. Multiple sets of RVEs were investigated under strain-controlled loading and periodic boundary conditions. The stress and strain contour maps obtained from RVEs with static mesh and grain-based mesh were compared. The simulation results reveal that both discretization methods provide reliable predictions of the stress-strain curves and the stress/strain localization points in polycrystalline alloys. Static mesh tends to smooth the stress/strain profile at the grain boundary, whilst stress/strain discontinuities are present in the grain-based mesh results. The above findings remain valid when the number of grains within an RVE increases from 34 to 1250. To quantify the difference between static and grain-based meshing, a relative measure of deviation is defined. The deviations of global stress were found to be relatively small, within 0.5%, while local deviations were significant up to 50%. Static mesh has the advantage of reducing both the preprocessing procedures and computational time compared to grain-based mesh. It is concluded that static mesh is preferred when investigating the material's macroscopic behaviour, whilst grain-based mesh is recommended for the study of the local response using CPFEM.

cond-mat.mtrl-sci

The creep deformation of a new nickel-base alloy-by-design studied using synchrotron X-ray diffraction

Understanding the creep mechanisms and deformation response at different stresses and temperatures is crucial for design using nickel-base superalloys for high-temperature applications. In this study, the creep behaviour of a newly designed superalloy (nominated Alloy 11) at different stress and temperature was systematically investigated using SEM, STEM, EBSD and synchrotron X-ray diffraction. Material properties and mechanical response were analysed by considering such properties as lattice parameters and misfit, phase volume fraction, microstrain in reference and crept samples. Detwinning and dynamic recrystallization were observed for the crept samples. STEM characterization of deformed materials reveals that multiple deformation mechanisms and defects could be identified in crept samples, namely, dislocations in the gamma matrix channels and in gamma prime precipitates, along with continuous and isolated stacking faults. The highest values of lattice misfit, microstrain and lattice parameter change were observed at the centre of dogbone-shaped crept samples. This was associated with the hump shaped temperature distribution profile during creep testing. The significant spatial variation detected in terms of lattice parameters, misfit and microstrain supports the conclusion that it is important to perform spatially resolved measurements instead of considering each sample as a single measurement point when investigating creep response. It is also worth noting that the statistics of the lattice-parameter distribution for the gamma and gamma prime phases obey a gaussian distribution. In conclusion, a discussion is given for the meaning and implications of these findings for future research.

cond-mat.mtrl-sci

The Yield Volume Fraction approach to the description of the stress-strain curve of a nickel-base superalloy

The stress-strain curves of most metallic alloys are often described using the relatively simple Ramberg-Osgood relationship. Whilst this description captures the overall stress-strain curve under monotonic tensile loading with reasonable overall accuracy, it often presents significant errors in the immediate post-yield region where the interplay between the elastic and plastic strains is particularly significant. This study proposes and develops a new approach to the description of the tensile stress-strain curve based on the Yield Volume Fraction (YVF) function. The YVF description provides an excellent match to experimental stress-strain curves based on a physically meaningful parameter that corresponds to the cumulative volume fraction of the polycrystal that undergoes yielding during monotonic deformation. The statistical nature of the polycrystal yield phenomenon is highlighted by the fact that the YVF model achieves good agreement with observations when the lognormal and extreme value distributions are employed to express the cumulative density function for the total yield volume fraction, and the probability density function for the incremental yield volume fraction, respectively. This proposed approach is compared with crystal plasticity finite element (CPFE) simulations and the Ramberg-Osgood model, along with experimental observations. The results highlight the potential of more extensive use of statistical methods in the description of material deformation response for improved design.

cond-mat.mtrl-sci

Monte Carlo studies of modified scalable designs for quantum computation

As the building blocks of topological quantum computation, Majorana zero modes (MZMs) have attracted tremendous attention in recent years. Scalable mesoscopic island designs with MZMs show great potential in quantum information processing. However, these systems are susceptible to quasi-particle poisoning which would induce various parity-breaking errors. To solve this problem, we modify the mesoscopic islands with gate-tunable valves and non-topological backbones. We study the lifetime of the Majorana qubits on these modified islands which are coupled to local bosonic and fermionic thermal baths. We consider both the parity-breaking and parity-preserving errors, and propose a parity correction scheme. By using Jordan-Wigner transformation, we analyze the probability of logical X and Y errors. The open quantum system is described by the Pauli master equation, and standard Monte Carlo simulations are applied to observe the behavior of the system when the parity correction proposal is implemented. The results demonstrate that (1) our parity correction proposal is effective to most of the parity-breaking errors; (2) the lifetime of the qubit benefits from larger island size before it meets the threshold; (3) small chemical potential $ μ$ on the non-topological backbones and fine tuned paring potential $ Δ$ of the topological bulk segment are required for high probability of correctness. Our results provide an effective error correction scheme for the parity-breaking errors.

cond-mat.mes-hall

SCAN: A Scalable Neural Networks Framework Towards Compact and Efficient Models

Remarkable achievements have been attained by deep neural networks in various applications. However, the increasing depth and width of such models also lead to explosive growth in both storage and computation, which has restricted the deployment of deep neural networks on resource-limited edge devices. To address this problem, we propose the so-called SCAN framework for networks training and inference, which is orthogonal and complementary to existing acceleration and compression methods. The proposed SCAN firstly divides neural networks into multiple sections according to their depth and constructs shallow classifiers upon the intermediate features of different sections. Moreover, attention modules and knowledge distillation are utilized to enhance the accuracy of shallow classifiers. Based on this architecture, we further propose a threshold controlled scalable inference mechanism to approach human-like sample-specific inference. Experimental results show that SCAN can be easily equipped on various neural networks without any adjustment on hyper-parameters or neural networks architectures, yielding significant performance gain on CIFAR100 and ImageNet. Codes will be released on github soon.

cs.LG

Be Your Own Teacher: Improve the Performance of Convolutional Neural Networks via Self Distillation

Convolutional neural networks have been widely deployed in various application scenarios. In order to extend the applications' boundaries to some accuracy-crucial domains, researchers have been investigating approaches to boost accuracy through either deeper or wider network structures, which brings with them the exponential increment of the computational and storage cost, delaying the responding time. In this paper, we propose a general training framework named self distillation, which notably enhances the performance (accuracy) of convolutional neural networks through shrinking the size of the network rather than aggrandizing it. Different from traditional knowledge distillation - a knowledge transformation methodology among networks, which forces student neural networks to approximate the softmax layer outputs of pre-trained teacher neural networks, the proposed self distillation framework distills knowledge within network itself. The networks are firstly divided into several sections. Then the knowledge in the deeper portion of the networks is squeezed into the shallow ones. Experiments further prove the generalization of the proposed self distillation framework: enhancement of accuracy at average level is 2.65%, varying from 0.61% in ResNeXt as minimum to 4.07% in VGG19 as maximum. In addition, it can also provide flexibility of depth-wise scalable inference on resource-limited edge devices.Our codes will be released on github soon.

cs.LG

The PSLQ Algorithm for Empirical Data

The celebrated integer relation finding algorithm PSLQ has been successfully used in many applications. PSLQ was only analyzed theoretically for exact input data, however, when the input data are irrational numbers, they must be approximate ones due to the finite precision of the computer. When the algorithm takes empirical data (inexact data with error bounded) instead of exact real numbers as its input, how do we theoretically ensure the output of the algorithm to be an exact integer relation? In this paper, we investigate the PSLQ algorithm for empirical data as its input. Firstly, we give a termination condition for this case. Secondly, we analyze a perturbation on the hyperplane matrix constructed from the input data and hence disclose a relationship between the accuracy of the input data and the output quality (an upper bound on the absolute value of the inner product of the exact data and the computed integer relation), which naturally leads to an error control strategy for PSLQ. Further, we analyze the complexity bound of the PSLQ algorithm for empirical data. Examples on transcendental numbers and algebraic numbers show the meaningfulness of our error control strategy.

cs.SC

Computing an LLL-reduced basis of the orthogonal lattice

As a typical application, the Lenstra-Lenstra-Lovasz lattice basis reduction algorithm (LLL) is used to compute a reduced basis of the orthogonal lattice for a given integer matrix, via reducing a special kind of lattice bases. With such bases in input, we propose a new technique for bounding from above the number of iterations required by the LLL algorithm. The main technical ingredient is a variant of the classical LLL potential, which could prove useful to understand the behavior of LLL for other families of input bases.

cs.SC

Front-to-End Bidirectional Heuristic Search with Near-Optimal Node Expansions

It is well-known that any admissible unidirectional heuristic search algorithm must expand all states whose $f$-value is smaller than the optimal solution cost when using a consistent heuristic. Such states are called "surely expanded" (s.e.). A recent study characterized s.e. pairs of states for bidirectional search with consistent heuristics: if a pair of states is s.e. then at least one of the two states must be expanded. This paper derives a lower bound, VC, on the minimum number of expansions required to cover all s.e. pairs, and present a new admissible front-to-end bidirectional heuristic search algorithm, Near-Optimal Bidirectional Search (NBS), that is guaranteed to do no more than 2VC expansions. We further prove that no admissible front-to-end algorithm has a worst case better than 2VC. Experimental results show that NBS competes with or outperforms existing bidirectional search algorithms, and often outperforms A* as well.

cs.AI

Multi-resonant piezoelectric shunting induced by digital controllers for subwavelength elastic wave attenuation in smart metamaterial

Instead of analog electronic circuits and components, digital controllers that are capable of active multi-resonant piezoelectric shunting are applied to elastic metamaterials integrated with piezoelectric patches. Giving thanks to the introduced digital control technique, shunting strategies with transfer functions that can hardly be realized with analog circuits is possible now. As an example, the "pole-zero" method is developed to design single- or multi-resonant bandgaps by adjusting poles and zeros in the transfer function of piezoelectric shunting directly. Large simultaneous attenuations in up to three frequency bands at deep subwavelength scale (with the normalized frequency as low as 0.077) are achieved. The underlying physical mechanism is attributed to the negative group velocity of flexural wave within bandgaps. As digital controllers can be readily adapted via wireless broadcasting, the bandgaps can be tuned easily instead of tuning the electric components in analog shunting circuits one by one manually. The theoretical results are well verified experimentally with the measured vibration transmission properties where large insulations of up to 20dB in low-frequency ranges are observed.

cond-mat.mtrl-sci

Deterministic generations of NOON states via shortcuts to adiabaticity

NOON states play the important roles in quantum information processings and quantum metrology, but the fidelities of these states generated previously are limited typically by the practically-unavoidable decoherence and operational imperfections. Here, we propose an efficient scheme to generate photonic NOON states alternatively by rapid population passage technique via shortcut to adiabaticity (STA), rather than the usual Rabi oscillations. Since the deterministic population passages based on the STAs are insensitive to details of the operations and can be implemented as fast as the Rabi oscillations, the fidelity of the generated NOON state could be satisfactorily high. The feasibility of the proposal is demonstrated specifically with the experimental circuit QED systems by rapidly driving two artifical qutrits.

quant-ph

A Short Note on Zero-error Computation for Algebraic Numbers by IPSLQ

The PSLQ algorithm is one of the most popular algorithm for finding nontrivial integer relations for several real numbers. In the present work, we present an incremental version of PSLQ. For some applications needing to call PSLQ many times, such as finding the minimal polynomial of an algebraic number without knowing the degree, the incremental PSLQ algorithm is more efficient than PSLQ, both theoretically and practically.

cs.SC

Detecting Simultaneous Integer Relations for Several Real Vectors

An algorithm which either finds an nonzero integer vector ${\mathbf m}$ for given $t$ real $n$-dimensional vectors ${\mathbf x}_1,...,{\mathbf x}_t$ such that ${\mathbf x}_i^T{\mathbf m}=0$ or proves that no such integer vector with norm less than a given bound exists is presented in this paper. The cost of the algorithm is at most ${\mathcal O}(n^4 + n^3 \log λ(X))$ exact arithmetic operations in dimension $n$ and the least Euclidean norm $λ(X)$ of such integer vectors. It matches the best complexity upper bound known for this problem. Experimental data show that the algorithm is better than an already existing algorithm in the literature. In application, the algorithm is used to get a complete method for finding the minimal polynomial of an unknown complex algebraic number from its approximation, which runs even faster than the corresponding \emph{Maple} built-in function.

cs.SC