var sms = '<div id="sms_bulletin">  <div id="sms_header">  <div class="do_not_print" id="arrow_left"><a href="?next=1"><img src="//www2.math.ethz.ch/smsjs/images/arrow_left.png"/></a></div><div class="do_not_print" id="arrow_right"><a href="?next=3"><img src="//www2.math.ethz.ch/smsjs/images/arrow_right.png"/></a></div>    <div class="sms_title">      <span style="float: left;">SMS</span>      <span>SWISS MATHEMATICAL SOCIETY</span>      <span style="float: right;">SMG</span>    </div>    <div class="sms_info">      <span style="float: left; width: 250px;">Bulletin no. 13</span>      <span style="float: right; text-align:right; width: 250px;">11.5 - 15.5.2026</span>      <span style="text-align: center; display: block; width: 250px; margin: auto; position: relative;">Spring Semester 2026</span>    </div>  </div>  <div></div>  <div id="sms_content">    <div class="day">      <div class="day_title">        Monday, May 11      </div>      <div class="day_content">        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://ethz.ch">ETH Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://math.ethz.ch/s/symplectic-geometry-seminar">Symplectic Geometry Seminar</a></div><br /><div class="event_speaker"> Beomjun Sohn (RWTH Aachen)</div><div class="event_title">Topological entropy under small area perturbation <span class="abstract-button do_not_print">abstract</span></div><div class="abstract-text" style="display: none"><strong>Abstract:</strong><br />In this talk, we present a new robustness result for the topological entropy of Hamiltonian diffeomorphisms on closed surfaces. Topological entropy is a fundamental measure of orbital complexity in dynamical systems, capturing chaotic behavior through a single non-negative value. We prove that if a Hamiltonian diffeomorphism has positive entropy, then any perturbation supported in a topological disk of sufficiently small area still has positive entropy. The proof relies on a new braid stability result derived from Floer-theoretic braids of fixed points, which can be related to the area of the support. This talk is based on ongiong joint work with Marcelo Alves and Matthias Meiwes.</div><div class="event_time">15:15 &bull; ETH Zentrum, R&auml;mistrasse 101, Z&uuml;rich, Building HG, Room G 43</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_ge"><a class="external" href="https://unige.ch">Université de Genève</a></div><div class="event_type"><a class="external" href="https://www.unige.ch/math/mpseminar/seminar.html">Séminaire de Mathématique Physique </a></div><br /><div class="event_speaker"> Erika  Roldan</div><div class="event_title">Title T.B.A.</div><div class="event_time">16:15 &bull; Université de Genève, Conseil Général 7-9, Room 1-15</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://ethz.ch">ETH Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://math.ethz.ch/sfs/news-and-events/data-science-seminar">ETH-FDS seminar </a></div><br /><div class="event_speaker"> Stefan  Steinerberger (UW Seattle)</div><div class="event_title">Particle Dynamics and Dimensionality Reduction <span class="abstract-button do_not_print">abstract</span></div><div class="abstract-text" style="display: none"><strong>Abstract:</strong><br />Dimensionality reduction, moving data from very high dimensions to intermediate dimensions, is well-established.  It is not too difficult to accurately map n points into ~log(n) dimensions.  The problem becomes a lot more difficult if one insists that the high-dimensional data be embedded into 2 dimensions which is what researchers in the biomedical fields need. Moreover, there are algorithms (most prominently tSNE and UMAP) that "semi-successfully" do this: they tend to work (though they also tend to fail on very simple examples).  An added difficulty is that it is difficult to assess from the output when they work.  I will argue that these algorithms reduce to understanding an attraction-repulsion functional acting on a large number of particles; this viewpoint immediately suggests new ideas and algorithms as well as a few benchmark problems.</div><div class="event_time">17:15 &bull; ETH Zentrum, R&auml;mistrasse 101, Z&uuml;rich, Building HG, Room F 3</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_be"><a class="external" href="https://www.unibe.ch">Universität Bern</a></div><div class="event_type"><a class="external" href="https://www.math.unibe.ch/research/talks/colloquium/index_eng.html">Mathematisches Kolloquium </a></div><br /><div class="event_speaker">Prof. Dr. Karl Worthmann (TU Illmenau)</div><div class="event_title"><a class="external" href="https://www.math.unibe.ch/research/talks/colloquium/index_eng.html">Data-driven surrogates of the Koopman operator</a> <span class="abstract-button do_not_print">abstract</span></div><div class="abstract-text" style="display: none"><strong>Abstract:</strong><br />Extended dynamic mode decomposition (EDMD), embedded in the Koopman framework, is a widely-applied data-driven technique to predict the evolution of observables along the flow of a nonlinear dynamical system. However, despite its popularity, the error analysis is still fragmentary. First, we provide an analysis of the error resulting from a finite dictionary size (projection) and finite data (estimation). Second, we indicate extensions towards reproducible kernel Hilbert spaces to establish L&#8734;-error bounds using kernel EDMD. Then, we leverage our findings to derive stability guarantees in predictive control despite using data-driven surrogate models in the optimization step.</div><div class="event_time">17:15 &bull; Universität Bern, Sidlerstrasse 5, 3012 Bern, Room B6</div>        </div>      </div>    </div>    <div class="day">      <div class="day_title">        Tuesday, May 12      </div>      <div class="day_content">        <div class="day_content_item normal"><div class="event_location uni_ba"><a class="external" href="https://unibas.ch">Universität Basel</a></div><div class="event_type"><a class="external" href="https://dmi.unibas.ch/de/forschung/mathematik/algebraische-geometrie/">Seminar Algebra and Geometry</a></div><br /><div class="event_speaker"> Saverio Secci (SISSA)</div><div class="event_title"><a class="external" href="https://dmi.unibas.ch/de/news-events/detail/seminar-algebra-and-geometry-saverio-secci-sissa/">Classification of Fano fourfolds with large anticanonical base locus.</a> <span class="abstract-button do_not_print">abstract</span></div><div class="abstract-text" style="display: none"><strong>Abstract:</strong><br />A famous theorem of Shokurov states that a general anticanonical divisor of a smooth Fano threefold is a smooth K3 surface. In a joint work with Andreas Höring we proved that for four-dimensional Fano manifolds the behaviour is completely opposite: if the anticanonical base locus is a normal surface, all the anticanonical divisors are singular. In this talk I will present our follow-up result, namely the classification of smooth Fano fourfolds with scheme-theoretic base locus a smooth surface: they form 22 families. I will also mention a result on elliptic Calabi-Yau threefolds that we obtained as a technical step in our study.</div><div class="event_time">10:30 &bull; Universität Basel, Spiegelgasse 5, Seminarraum 05.002</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_ge"><a class="external" href="https://unige.ch">Université de Genève</a></div><div class="event_type"><a class="external" href="https://www.unige.ch/math/annonces/seminaire-danalyse-numerique">Séminaire d\'Analyse Numérique </a></div><br /><div class="event_speaker"> Jörg Nick</div><div class="event_title">Regularized dynamical parametric approximation of stiff evolution problems <span class="abstract-button do_not_print">abstract</span></div><div class="abstract-text" style="display: none"><strong>Abstract:</strong><br />Parametric approaches numerically approximate the solution of evolution equations by nonlinear parametrizations u(t) = \\Phi( q (t)) with time-dependent parameters q(t), which are to be determined in the computation. The talk discusses numerical integrators for the resulting evolution problems for the evolving parameters q(t). The primary focus is on tackling the challenges posed by the combination of stiff evolution problems and irregular parametrizations, which typically arise with neural networks, tensor networks, flocks of evolving Gaussians, and in further cases of overparametrization. Regularized parametric versions of classical time stepping schemes for the time integration of the parameters in nonlinear approximations to evolutionary partial differential equations are presented. At each time step, an ill-conditioned nonlinear optimization problem is solved approximately with a few regularized Gauß--Newton iterations. Error bounds for the resulting parametric integrator are shown. Numerical experiments that are designed to show key properties of the proposed parametric integrators are discussed.</div><div class="event_time">14:00 &bull; Université de Genève, Conseil Général 7-9, Room 1-05</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://ethz.ch">ETH Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://math.ethz.ch/s/analysis-seminar">Analysis Seminar</a></div><br /><div class="event_speaker">Dr. Massimo Sorella (Imperial College London)</div><div class="event_title">Title T.B.A.</div><div class="event_time">15:15 &bull; ETH Zentrum, R&auml;mistrasse 101, Z&uuml;rich, Building HG, Room G 43</div>        </div>      </div>    </div>    <div class="day">      <div class="day_title">        Wednesday, May 13      </div>      <div class="day_content">        <div class="day_content_item normal"><div class="event_location uni_la"><a class="external" href="https://www.epfl.ch">EPF Lausanne</a></div><div class="event_type"><a class="external" href="https://calendar.google.com/calendar/embed?mode=AGENDA&height=600&wkst=2&bgcolor=%23FFFFFF&src=t36it03v52cus2detrvinlgk18%40group.calendar.google.com&color=%235F6B02&ctz=Europe%2FZurich">Groups, Arithmetic and Algebraic Geometry Seminar </a></div><br /><div class="event_speaker"> Matteo Tamiozzo</div><div class="event_title">Title T.B.A.</div><div class="event_time">10:00 &bull; EPF Lausanne</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://ethz.ch">ETH Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://www.math.uzh.ch/mat760">Ergodic theory and dynamical systems seminar</a></div><br /><div class="event_speaker">Prof. Dr. Marco Lenci (University of Bologna)</div><div class="event_title">Title T.B.A.</div><div class="event_time">13:30 &bull; ETH Zentrum, R&auml;mistrasse 101, Z&uuml;rich, Building HG, Room G 19.1</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://ethz.ch">ETH Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://math.ethz.ch/s/geometry-seminar">Geometry Seminar</a></div><br /><div class="event_speaker"> Daniela Paiva Peñuela (Universität Basel)</div><div class="event_title">Title T.B.A.</div><div class="event_time">15:30 &bull; ETH Zentrum, R&auml;mistrasse 101, Z&uuml;rich, Building HG, Room G 43</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://uzh.ch">Universit&auml;t Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://www.math.uzh.ch/mat675.1">PDE and Mathematical Physics</a></div><br /><div class="event_speaker">Prof. Dr. Yan Guo (Brown University)</div><div class="event_title">Gravitational Collapse of Gaseous Stars <span class="abstract-button do_not_print">abstract</span></div><div class="abstract-text" style="display: none"><strong>Abstract:</strong><br />&lt;p>We review recent progress in the PDE study of gravitational collapse in both Newtonian as well as relativistic contexts.&lt;/p></div><div class="event_time">16:15 &bull; UZH Irchel, Winterthurerstrasse 190, Z&uuml;rich, Building Y27, Room H 35/36</div>        </div>      </div>    </div>    <div class="day">      <div class="day_title">        Thursday, May 14      </div>      <div class="day_content">        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://ethz.ch">ETH Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://math.ethz.ch/fim/activities/nachdiplom-lectures">Nachdiplomvorlesung</a></div><br /><div class="event_speaker"> Sylvain Crovisier (Université Paris-Saclay)</div><div class="event_title">Ergodic theory of surface diffeomorphisms</div><div class="event_time">10:15 &bull; ETH Zentrum, R&auml;mistrasse 101, Z&uuml;rich, Building HG, Room G 43</div>        </div>      </div>    </div>    <div class="day">      <div class="day_title">        Friday, May 15      </div>      <div class="day_content">        <div class="day_content_item normal"><div class="event_location uni_zh"><a class="external" href="https://ethz.ch">ETH Z&uuml;rich</a></div><div class="event_type"><a class="external" href="https://math.ethz.ch/fim/activities/nachdiplom-lectures">Nachdiplomvorlesung</a></div><br /><div class="event_speaker"> Tom Hutchcroft (California Institute of Technology (Caltech))</div><div class="event_title">Dimension dependence of critical phenomena in percolation</div><div class="event_time">10:15 &bull; ETH Zentrum, R&auml;mistrasse 101, Z&uuml;rich, Building HG, Room G 43</div>        </div>        <div class="day_content_item normal"><div class="event_location uni_ge"><a class="external" href="https://unige.ch">Université de Genève</a></div><div class="event_type"><a class="external" href="https://sites.google.com/view/pm-seminar/home">Physical Mathematics Seminar</a></div><br /><div class="event_speaker"> Kohei Iwaki</div><div class="event_title">Title T.B.A.</div><div class="event_time">14:00 &bull; Université de Genève, Conseil Général 7-9, Room 8-08</div>        </div>      </div>    </div>  </div>  <div id="sms_footer">    address: Alessandra Naldi Windler, Departement Mathematik, HG G 51.4, ETH Zurich, Raemistrasse 101, CH-8092 Zurich<br />    email: <a href="mailto:bulletin@math.ch">bulletin@math.ch</a> | phone: +41 44 632 3684 | url: <a href="https://math.ch">https://math.ch</a>    <br /><br /><img src="//www2.math.ethz.ch/smsjs/sms_logo.gif" width="150" alt="SMS/SMG Logo" title="SMS/SMG Logo" />  </div></div>';