BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Namur Institute For Complex Systems - ECPv6.15.14//NONSGML v1.0//EN CALSCALE:GREGORIAN METHOD:PUBLISH X-ORIGINAL-URL:https://www.naxys.be X-WR-CALDESC:Events for Namur Institute For Complex Systems REFRESH-INTERVAL;VALUE=DURATION:PT1H X-Robots-Tag:noindex X-PUBLISHED-TTL:PT1H BEGIN:VTIMEZONE TZID:Europe/Brussels BEGIN:DAYLIGHT TZOFFSETFROM:+0100 TZOFFSETTO:+0200 TZNAME:CEST DTSTART:20230326T010000 END:DAYLIGHT BEGIN:STANDARD TZOFFSETFROM:+0200 TZOFFSETTO:+0100 TZNAME:CET DTSTART:20231029T010000 END:STANDARD BEGIN:DAYLIGHT TZOFFSETFROM:+0100 TZOFFSETTO:+0200 TZNAME:CEST DTSTART:20240331T010000 END:DAYLIGHT BEGIN:STANDARD TZOFFSETFROM:+0200 TZOFFSETTO:+0100 TZNAME:CET DTSTART:20241027T010000 END:STANDARD BEGIN:DAYLIGHT TZOFFSETFROM:+0100 TZOFFSETTO:+0200 TZNAME:CEST DTSTART:20250330T010000 END:DAYLIGHT BEGIN:STANDARD TZOFFSETFROM:+0200 TZOFFSETTO:+0100 TZNAME:CET DTSTART:20251026T010000 END:STANDARD END:VTIMEZONE BEGIN:VEVENT DTSTART;TZID=Europe/Brussels:20241115T130000 DTEND;TZID=Europe/Brussels:20241115T140000 DTSTAMP:20260406T171228 CREATED:20241030T101730Z LAST-MODIFIED:20241106T122335Z UID:2224-1731675600-1731679200@www.naxys.be SUMMARY:Serge Gratton (Toulouse INP) DESCRIPTION:Title : Adaptive regularization algorithms for Objective-Function-Free Optimization \nAbstract : \nThis work is about the fastest known optimization method in terms of complexity\, which does not require the evaluation of the objective function. Such methods\, termed Objective-Function-Free Optimization (OFFO)\, have gained popularity recently\, especially in noisy problem contexts\, including deep learning applications. We present an adaptive regularization OFFO algorithm for unconstrained nonconvex optimization. This algorithm is part of the adaptive regularization methods family\, which is known for its optimal worst-case complexity results in the conventional framework where the objective function is evaluated. We demonstrate that these outstanding complexity bounds are maintained with the new algorithm\, even though it relies on significantly less information. Specifically\, we show that using derivatives of degree one to p\, the algorithm will find an š¯›†1-approximate first-order minimizer in at most O(š¯›†-(p+1)/p) iterations\, and an (š¯›†1\, š¯›†2)-approximate second-order minimizer in at most O(š¯›†-(p+1)/p\, š¯›†-(p+1)/(p-1)}) iterations. As a particular case\, the algorithm\, when using first and second derivatives and applied to functions with Lipschitz continuous Hessian\, will find an iterate xk where the gradientā€™s norm is less than š¯›†1 in at most O(š¯›†-3/2) iterations. Numerical experiments demonstrate the excellent performance of this method for noisy problems\, highlighting its robustness and efficiency across various scenarios. \nThe seminar will take place in Room S08 at the Faculty of Sciences. URL:https://www.naxys.be/event/serge-gratton-toulouse-inp/ CATEGORIES:NAXYS Seminar END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Brussels:20241121T130000 DTEND;TZID=Europe/Brussels:20241121T140000 DTSTAMP:20260406T171228 CREATED:20241015T083607Z LAST-MODIFIED:20241118T101801Z UID:2203-1732194000-1732197600@www.naxys.be SUMMARY:Maxime Lucas (UNamur/UCLouvain) DESCRIPTION:Title : Of higher-order interactions\, whales\, and fungi \nAbstract :Ā  \nThe strength of dynamical systems and network models lies in their ability to represent diverse systems that\, despite their apparent differences\, rely on common mechanisms. In this talk\, I will share insights from three of my primary research areas. First\, we will explore how higher-order interactionsā€”those involving any number of unitsā€”extend beyond traditional networks to impact the synchronisation of oscillators. In particular\, I will discuss how the two most common representations of higher-order interactions\, hypergraphs and simplicial complexes\, can have opposing effects on synchrony stability. We will also see how these interactions can reduce the basin of attraction for synchronised states while enhancing their linear stability\, resulting in more stable yet narrower basins. Second\, I will introduce Project CETI\, a multi-disciplinary collaboration focused on understanding sperm whale communication. Here\, we will look at how factors like kinship and shared territories influence their communicative behaviors and social interactions. Finally\, we will discuss underground fungal networks\, specifically those of arbuscular mycorrhizal fungi. These fungi form extensive hyphal networks that connect to plant roots\, facilitating resource exchanges and enhancing ecosystem resilience. We are interested in characterising the structural properties and robustness of these vital networks. \nThe seminar will take place in Room S07 at the Faculty of Sciences. URL:https://www.naxys.be/event/maxime-lucas-unamur-uclouvain/ CATEGORIES:NAXYS Seminar END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Brussels:20241126T130000 DTEND;TZID=Europe/Brussels:20241126T140000 DTSTAMP:20260406T171228 CREATED:20241017T120934Z LAST-MODIFIED:20241121T163750Z UID:2216-1732626000-1732629600@www.naxys.be SUMMARY:Hidemasa Ishii (University of Tokyo) DESCRIPTION:Title : Employing dynamical modeling to understand complex phenomena: from interacting bistable systems to football ball possession \nAbstract : \nI have been motivated to employ dynamical modeling to understand complex phenomena in social sciences and biology.\nIn this seminar\, I would like to introduce two projects I have worked on.\nThe first involves a system of diffusively coupled bistable elements\, which have been utilized to study abrupt transitions in complex systems.\nWe analysed the influence of coupling strength over the mean escape time.\nWe numerically found that weak coupling facilitates escape on average\, while strong coupling impedes escape [1].\nWe argue\, although diffusive coupling both facilitates and impedes escape\, the facilitating effect is dominant under weak coupling.\nThe second topic concerns dynamical modelling for three-versus-one ball possession in football.\nIn our model\, motion of the players and ball is governed by a system of ODEs during a single pass.\nThe model is nevertheless stochastic\, because the initial condition and parameters of the ODEs depend probabilistically on the final state of the previous pass.\nWe aim to utilize this approach to quantify the difference between high- and lower-level football teams. \n[1] H. Ishii and H. Kori\, Diffusive coupling facilitates and impedes noise-induced escape in interacting bistable elements\, Sci Rep 14\, 11019 (2024). \nThe seminar will take place in Room S07 at the Faculty of Sciences. URL:https://www.naxys.be/event/hidemasa-ishii-university-of-tokyo/ CATEGORIES:NAXYS Seminar END:VEVENT BEGIN:VEVENT DTSTART;TZID=Europe/Brussels:20241128T130000 DTEND;TZID=Europe/Brussels:20241128T140000 DTSTAMP:20260406T171228 CREATED:20241017T121012Z LAST-MODIFIED:20241107T192521Z UID:2218-1732798800-1732802400@www.naxys.be SUMMARY:Yusuke Kato (University of Tokyo) DESCRIPTION:Title : Introduction of two studies: (1) analysis of oscillation quenching by periodic perturbation and (2) parameter estimation of Kuramoto model \nAbstract :Ā  \nI will talk about the two different projects that I am working on in Japan. (1) In the first part\, I will present the oscillation quenching (annihilation of oscillation) inĀ aĀ bistable oscillatorĀ model [1]. We find that multiplicative periodic forces combined with feedback induceĀ quenching and perform the bifurcation analysis usingĀ anĀ averaging approximation. (2) The second part would be about the parameter estimation of the Kuramoto model\, which is a mathematical model that describes synchronization phenomena. We use the time series of the order parameter (a macroscopic quantity that characterizes how the whole population is synchronized) as given data and estimate the model parameters. The estimation is performed by the Bayesian approach\, using the exchage Monte Carlo method for computation.Ā \n\n[1] Y. Kato and H. Kori. Periodic forces combined with feedback induce quenching in a bistable oscillator. Chaos 34\, 103125 (2024).\n\nThe seminar will take place in Room S08 at the Faculty of Sciences. URL:https://www.naxys.be/event/yusuke-kato-university-of-tokyo/ CATEGORIES:NAXYS Seminar END:VEVENT END:VCALENDAR