Akifumi Okuno

ORCID: 0000-0001-9621-8853
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About
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Research Areas
  • Advanced Graph Neural Networks
  • Statistical Methods and Inference
  • Neural Networks and Applications
  • Domain Adaptation and Few-Shot Learning
  • Face and Expression Recognition
  • Advanced Statistical Methods and Models
  • Complex Network Analysis Techniques
  • Model Reduction and Neural Networks
  • Bayesian Methods and Mixture Models
  • Machine Learning and ELM
  • Sparse and Compressive Sensing Techniques
  • Tensor decomposition and applications
  • Stellar, planetary, and galactic studies
  • Bioinformatics and Genomic Networks
  • Machine Learning and Algorithms
  • Topic Modeling
  • Gaussian Processes and Bayesian Inference
  • Image Retrieval and Classification Techniques
  • Astronomy and Astrophysical Research
  • Stochastic Gradient Optimization Techniques
  • Forecasting Techniques and Applications
  • Advanced Causal Inference Techniques
  • Magnetic confinement fusion research
  • Neural Networks and Reservoir Computing
  • Machine Learning in Materials Science

The Institute of Statistical Mathematics
2022-2025

RIKEN Center for Advanced Intelligence Project
2018-2024

Kyoto University
2018-2020

Osaka University
2016

We propose a systematic approach for decomposing numerical turbulence fields with both low and high degrees of freedom, extending beyond the conventional division into zonal flow turbulence. Specifically, we utilize Fourier expansion to decompose several substructures where phase kinetic energy density aligns positively or negatively flow's poloidal velocity, enabling separation expected be absorbed flow. The proposed methods were successfully applied simulation datasets generated,...

10.1063/5.0256907 article EN Physics of Plasmas 2025-03-01

Abstract R -process enhanced stars with [Eu/Fe] ≥ +0.7 (so-called r -II stars) are believed to have formed in an extremely neutron-rich environment which a rare astrophysical event (e.g., neutron-star merger) occurred. This scenario is supported by the existence of ultra-faint dwarf galaxy, Reticulum II, where most highly elements. In this scenario, some small fraction galaxies around Milky Way were enhanced. When each r-enhanced galaxy accreted Way, it deposited many Galactic halo similar...

10.3847/1538-4357/acb93b article EN cc-by The Astrophysical Journal 2023-03-01

10.1007/s10463-024-00906-9 article EN Annals of the Institute of Statistical Mathematics 2024-05-02

A simple framework Probabilistic Multi-view Graph Embedding (PMvGE) is proposed for multi-view feature learning with many-to-many associations so that it generalizes various existing methods. PMvGE a probabilistic model predicting new via graph embedding of the nodes data vectors links their associations. are transformed by neural networks to in shared space, and probability association between two modeled inner product vectors. While techniques can treat only either or non-linear...

10.48550/arxiv.1802.04630 preprint EN other-oa arXiv (Cornell University) 2018-01-01

We propose weighted inner product similarity (WIPS) for neural network-based graph embedding. In addition to the parameters of networks, we optimize weights by allowing positive and negative values. Despite its simplicity, WIPS can approximate arbitrary general similarities including definite, conditionally indefinite kernels. is free from model selection, since it learn any models such as cosine similarity, Poincaré distance Wasserstein distance. Our experiments show that proposed method...

10.24963/ijcai.2019/699 article EN 2019-07-28

A large number of images are available on online photo-sharing services along with rich meta-data, including tags, groups, and locations, etc. For associating two domains different modalities, e.g. Canonical Correlation Analysis (CCA) its extended methods used widely. We employ a more flexible graph embedding method called Cross-Domain Matching (CDMCA), which can deal many-to-many relationships between any domains, for images, groups. Experiments Tag-to-Image Image-to-Tag retrieval tasks...

10.1109/icip.2016.7532351 article EN 2022 IEEE International Conference on Image Processing (ICIP) 2016-08-17

10.1016/j.neunet.2020.03.026 article EN Neural Networks 2020-04-02

We propose $β$-graph embedding for robustly learning feature vectors from data and noisy link weights. A newly introduced empirical moment $β$-score reduces the influence of contamination measures difference between underlying correct expected weights links specified generative model. The proposed method is computationally tractable; we employ a minibatch-based efficient stochastic algorithm prove that this locally minimizes $β$-score. conduct numerical experiments on synthetic real-world datasets.

10.48550/arxiv.1902.08440 preprint EN other-oa arXiv (Cornell University) 2019-01-01

This study proposes an interpretable neural network-based non-proportional odds model (N$^3$POM) for ordinal regression. N$^3$POM is different from conventional approaches to regression with models in several ways: (1) defined both continuous and discrete responses, whereas standard methods typically treat the ordered variables as if they are discrete, (2) instead of estimating response-dependent finite-dimensional coefficients linear responses done approaches, we train a non-linear network...

10.48550/arxiv.2303.17823 preprint EN other-oa arXiv (Cornell University) 2023-01-01

This study delves into the domain of dynamical systems, specifically forecasting time series defined through an evolution function. Traditional approaches in this area predict future behavior systems by inferring However, these methods may confront obstacles due to presence missing variables, which are usually attributed challenges measurement and a partial understanding system interest. To overcome obstacle, we introduce autoregressive with slack (ARS) model, that simultaneously estimates...

10.1109/access.2024.3365724 article EN cc-by-nc-nd IEEE Access 2024-01-01

This paper presents an integrated perspective on robustness in regression. Specifically, we examine the relationship between traditional outlier-resistant robust estimation and optimization, which focuses parameter resistant to imaginary dataset-perturbations. While both are commonly regarded as methods, these concepts demonstrate a bias-variance trade-off, indicating that they follow roughly converse strategies.

10.48550/arxiv.2407.10418 preprint EN arXiv (Cornell University) 2024-07-14

We study a minimax risk of estimating inverse functions on plane, while keeping an estimator is also invertible. Learning invertibility from data and exploiting invertible are used in many domains, such as statistics, econometrics, machine learning. Although the consistency universality estimators have been well investigated, analysis efficiency these methods still under development. In this study, we for bi-Lipschitz square 2-dimensional plane. first introduce two types L2-risks to evaluate...

10.1214/23-ejs2202 article EN cc-by Electronic Journal of Statistics 2024-01-01

This study proposes an interpretable neural network-based nonproportional odds model (N3POM) for ordinal regression. N3POM is different from conventional approaches to regression with models in several ways: (a) defined both continuous and discrete responses, whereas standard methods typically treat the variables as if they were discrete, (b) instead of estimating response-dependent finite-dimensional coefficients linear responses done approaches, we train a nonlinear network serve...

10.1080/10618600.2024.2321208 article EN Journal of Computational and Graphical Statistics 2024-02-22

We propose shifted inner-product similarity (SIPS), which is a novel yet very simple extension of the ordinary (IPS) for neural-network based graph embedding (GE). In contrast to IPS, that limited approximating positive-definite (PD) similarities, SIPS goes beyond limitation by introducing bias terms in IPS; we theoretically prove capable not only PD but also conditionally (CPD) similarities with many examples such as cosine similarity, negative Poincare distance and Wasserstein distance....

10.48550/arxiv.1810.03463 preprint EN other-oa arXiv (Cornell University) 2018-01-01

$R$-process enhanced stars with [Eu/Fe]$\geq+0.7$ (so-called $r$-II stars) are believed to have formed in an extremely neutron-rich environment which a rare astrophysical event (e.g., neutron star merger) occurred. This scenario is supported by the existence of ultra-faint dwarf galaxy, Reticulum~II, where most highly $r$-process elements. In this scenario, some small fraction galaxies around Milky Way were $r$ enhanced. When each $r$-enhanced galaxy accreted Way, it deposited many Galactic...

10.48550/arxiv.2207.04110 preprint EN other-oa arXiv (Cornell University) 2022-01-01

We propose $\textit{weighted inner product similarity}$ (WIPS) for neural network-based graph embedding. In addition to the parameters of networks, we optimize weights by allowing positive and negative values. Despite its simplicity, WIPS can approximate arbitrary general similarities including definite, conditionally indefinite kernels. is free from similarity model selection, since it learn any models such as cosine similarity, Poincar\'e distance Wasserstein distance. Our experiments show...

10.48550/arxiv.1902.10409 preprint EN other-oa arXiv (Cornell University) 2019-01-01

This paper discusses the estimation of generalization gap, difference between performance and training performance, for overparameterized models including neural networks. We first show that a functional variance, key concept in defining widely-applicable information criterion, characterizes gap even settings where conventional theory cannot be applied. As computational cost variance is expensive models, we propose an efficient approximation function Langevin (Langevin FV). method leverages...

10.1080/10618600.2023.2197488 article EN cc-by-nc-nd Journal of Computational and Graphical Statistics 2023-04-04

This study delves into the domain of dynamical systems, specifically forecasting time series defined through an evolution function. Traditional approaches in this area predict future behavior systems by inferring However, these methods may confront obstacles due to presence missing variables, which are usually attributed challenges measurement and a partial understanding system interest. To overcome obstacle, we introduce autoregressive with slack (ARS) model, that simultaneously estimates...

10.48550/arxiv.2306.16593 preprint EN other-oa arXiv (Cornell University) 2023-01-01

Density power divergence (DPD) is designed to robustly estimate the underlying distribution of observations, in presence outliers. However, DPD involves an integral parametric density models be estimated; explicit form term can derived only for specific densities, such as normal and exponential densities. While we may perform a numerical integration each iteration optimization algorithms, computational complexity has hindered practical application DPD-based estimation more general To address...

10.48550/arxiv.2307.05251 preprint EN other-oa arXiv (Cornell University) 2023-01-01

While highly expressive parametric models including deep neural networks have an advantage to model complicated concepts, training such non-linear is known yield a high risk of notorious overfitting. To address this issue, study considers $(k,q)$th order variation regularization ($(k,q)$-VR), which defined as the $q$th-powered integral absolute $k$th derivative be trained; penalizing $(k,q)$-VR expected smoother function, avoid Particularly, encompasses conventional (general-order) total...

10.48550/arxiv.2308.02293 preprint EN other-oa arXiv (Cornell University) 2023-01-01

\'Cwik and Mielniczuk (1989) introduced a univariate kernel density ratio estimator, which directly estimates the without estimating two densities of interest. This study presents its straightforward multivariate adaptation.

10.48550/arxiv.2311.12380 preprint EN other-oa arXiv (Cornell University) 2023-01-01
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