# Esitelmiä, seminaareja ja väitöksiä

* Seuraavan viikon tapahtumat merkitty tähdellä

Younis Bouzar

**Sparse Grid Interpolation (Bachelor thesis talk)**

*** ** Monday 05 June 2023, 13:15, M3 (M234)

Prof. Marcus Greferath (University College Dublin)

**On current work in Group Testing with Error-Correction Capabilities**

*** ** Wednesday 07 June 2023, 16:15, M3 (M234)

During the years of the COVID19 pandemic my collaborators and I have tried to revisit and possibly remodel the discipline of group testing in such a way, that it can be seen as a finite linear algebra over the binary semifield. Residuation Theory as presented in a textbook by T. S. Blyth and M. F. Janowitz plays a prominent role in our account on this topic, and we will also attempt to address the error-prone part. The presentation will be complemented by a number of examples.

ANTA Seminar / Hollanti et al.

Dr. Ali Abbas (University of Southern California)

**Ethical Decision Quality: Avoiding Common Pitfalls in Organizational Decision-Making **

*** ** Thursday 08 June 2023, 16:00, M1 (M232)

Further information

This talk first demonstrates numerous examples of situations where business organizations and government agencies did the right thing in terms of gathering information or conducting some analyses, but then ended up making bad decisions. By examining a sequence of decisions from publicly available sources in business and government enterprises, the talk characterizes 11 elements to be considered when making "Good" organizational decisions. We refer to those elements as the Elements of Ethical Decision Quality. The talk then presents specific examples of decisions where the Elements of Ethical Decision Quality created value by either improving the quality of the decisions or by providing awareness to policymakers about the implications of the current decision-making process. These examples include work with the U.S. Transportation and Security Administration (TSA), U.S. Customs and Border Protection (CBP), and NASA.
The event can also be attended remotely on Zoom here: https://aalto.zoom.us/j/68625209279

Aalto Systems Forum / Ahti Salo (Systems Analysis Laboratory)

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Friday 16 June 2023, 09:30, Riihi (Y225a)

Further information

Dr. Amin Sakzad (Monash University)

**Vandermonde meets Regev: Public Key Encryption Schemes Based on Partial Vandermonde Problems**

Wednesday 12 July 2023, 15:15, M3 (M234)

ANTA Seminar / Hollanti et al.

## Past events

Dr. Alberto Pedrouzo Ulloa (U. Vigo)

**Disrespectfully playing with Homomorphic Encryption, Federated Learning and Multivariate Rings**

Wednesday 31 May 2023, 10:15, M3 (M234)

In this talk we will discuss some of the benefits and shortcomings of using Homomorphic Encryption (HE) for two very different types of practical applications. Firstly, we will talk about Federated Learning, and how to tailor HE for the efficient execution of secure average aggregation. In the last part of the talk, we will modify current HE schemes with the objective of better dealing with privacy-sensitive multidimensional signals (e.g., images). In particular, we will explore the possibility of substituting the more conventional power-of-two cyclotomic rings for different types of multivariate rings.

ANTA Seminar / Hollanti et al.

Prof. Gunnar Fløystad (University of Bergen)

**Polarizations of artin monomial ideals define triangulated balls**

Monday 29 May 2023, 15:15, Zoom

We show that any polarization of an artin monomial ideal
defines a triangulated ball, via the Stanley-Reisner correspondence.
This proves a conjecture of A.Almousa, H.Lohne and the speaker.
Geometrically, polarizations of ideals containing the ideal (x_1^{a_1}, ...., x_n^{a_n})
define full-dimensional triangulated balls on the sphere which is the join of boundaries of simplices of dimensions a_1-1, ... , a_n-1.
Combinatorially, these triangulated balls derive from subsets T of products of finite sets A_1 x A_2 x ... x A_n which we call bitight. The subset T and its complement fulfill exchange conditions similar to that of matroids.
Zoom link: https://aalto.zoom.us/j/64355991428

Algebra and Discrete Mathematics Seminar

Ville Turunen

**Diophantine equation (n+1)x^2-ny^2 = 1 in time-frequency analysis**

Wednesday 24 May 2023, 16:15, Y307

We introduce and study Diophantine equation (n+1)x^2-ny^2 = 1. It resembles the more complicated Lagrange's theory of Pell's equation x^2-ny^2=1. Positive n \in Z is called P-smooth if its prime factors belong to a subset P of the primes. In tonal music, the melodic intervals n: (n+1) are nearly always {2,3,5,7}-smooth. In 1897, Størmer used Pell's equation to find the P-smooth pairs (n,n+1). We give a simple well-motivated method for Størmer's problem.

ANTA Seminar / Hollanti et al.

Petteri Kaski (Aalto)

**Constructive and nonconstructive enumeration**

Monday 22 May 2023, 15:15, M2 (M233)

This talk will be a primer to combinatorial constructive and nonconstructive enumeration up to isomorphism and will consist of two parts (a) a recall/primer of finite groups and group actions to capture pertinent isomorphism relations and (b) an introduction to algorithmic isomorph-free exhaustive generation techniques, in particular to Brendan McKay's [J Algorithms 1998] influential canonical construction path technique.

Algebra and discrete mathematics seminar

Anton Vavilov (Aalto University)

**Implementing Electrical Impedance Tomography for Real-World Stroke Monitoring (Doctoral Midterm Review)**

Wednesday 17 May 2023, 13:30, M203

Tuomas Kelomäki (Aalto University)

**Discrete Morse theory for Khovanov homology (Doctoral Midterm Review)**

Wednesday 17 May 2023, 13:00, M203

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Tuesday 16 May 2023, 09:30, Riihi (Y225a)

Further information

Irene Heinrich (TU Darmstadt)

**Colored highly regular graphs**

Monday 15 May 2023, 15:15, M2 (M233)

A coloured graph is k-ultrahomogeneous if every isomorphism between two induced subgraphs of order at most k extends to an automorphism. A coloured graph is t-tuple regular if the number of vertices adjacent to every vertex in a set S of order at most k depends only on the isomorphism type of the subgraph induced by S. We classify the finite vertex-coloured k-ultrahomogeneous graphs and the finite vertex-coloured l-tuple regular graphs for k at least 4 and l at least 5, respectively. Our theorem in particular classifies finite vertex-coloured ultrahomogeneous graphs, where ultrahomogeneous means the graph is simultaneously k-ultrahomogeneous for all k.

Algebra and discrete mathematics seminar

**Matematiikan kandiseminaari (Bachelor thesis seminar in Math.)**

Friday 12 May 2023, 09:00, M3 (M234)

Further information

Prof. Giacomo Micheli (U. South Florida)

**On a proof of a conjecture on Arboreal Galois Representations**

Thursday 11 May 2023, 16:15, M3 (M234)

In this talk we first recall the notion of arboreal Galois representation and then we develop a method to effectively determine the set of primes p for which certain arboreal Galois representations are surjective modulo p.
Our method is based on a combination of height bounds on integral points on elliptic curves over function fields in positive characteristic and the ABC theorem for function fields.
Using this technique we prove Jones' conjecture on the surjectivity of the arboreal Galois representation attached to f=x^2+t [Conjecture 6.7, Compositio Math. 43 (5) (2007)].
This is a joint work with Andrea Ferraguti.

ANTA Seminar / Hollanti et al.

Zichan Xie (Aalto University)

**District heating system - dynamic simulation and optimization (Doctoral Midterm Review)**

Thursday 11 May 2023, 13:30, M203

Jaakko Pere (Aalto University)

**On extreme behavior of multivariate and infinite dimensional observations (Doctoral Midterm Review)**

Thursday 11 May 2023, 13:00, M203

Prof. Federico Poloni (University of Pisa)

**Centrality measures on Markov chains, with applications to roads and infection models**

Tuesday 09 May 2023, 15:15, M1 (M232)

We describe a couple of centrality measures on graphs that can be obtained from certain Markov chain models associated to them, and their computation with methods taken from numerical linear algebra.
The Kemeny constant is a quantity that measures the connectedness of a Markov chain by studying certain properties of the random walk associated to it. The variation in the Kemeny constant can be used to identify edges whose removal would alter the connectivity of a network; this is useful information, for instance, in planning urban and regional road networks.
For problems based on "spreading" on a graph, such as news propagation and infectious disease modelling, instead models based on a single random walker fall short: they are unable to capture characteristics of the model such as the time to saturation. We study this phenomenon, and propose an alternative way to treat computationally the full model, which can be interpreted as another Markov chain with an exponential
number of states. The resulting metric can once again be interpreted as a measure of the centrality of the vertices / agents in the network in the propagation.

Lasse Leskelä

**Information-theoretic limits in inhomogeneous random hypergraphs**

Tuesday 09 May 2023, 10:30, M3 (M234)

The hypergraph stochastic block model is a statistical model for sampling inhomogeneous random hypergraphs associated with a partition of the vertex set. In this talk I will discuss fundamental concepts and recent developments on the statistical analysis of hypergraph stochastic block models. The focus is on universal information-theoretic bounds and phase transitions that help to understand requirements on data sparsity and model dimensions under which consistent learning of the underlying vertex partition is possible.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Prof. Emer. Brendan D McKay (Australian National University)

**A scientist's adventure into pseudoscience: the strange case of the Bible Codes**

Thursday 04 May 2023, 15:15, M2 (M233)

Further information

Over the centuries, many claims have been made of numerical patterns of miraculous nature hidden within the text of sacred writings, including the Jewish, Christian and Islamic scriptures. Usually the patterns involve counting of letters and words, or calculations involving numerical equivalents of the letters.
Until recently, all such claims were made by people with little mathematical understanding and were easily explained. This situation changed when a highly respected Israeli mathematician Eliyahu Rips and two others published a paper in the academic journal Statistical Science claiming to prove that information about medieval Jewish rabbis was encoded in the Hebrew text of the Book of Genesis. The journal reported that its reviewers were "baffled".
The paper in Statistical Science spawned a huge "Bible Codes" industry, complete with best selling books, TV documentaries, and even a romance movie.
The talk will reveal the inside story of the Codes and the people behind them, from their inception through to their refutation.

Aalto Stochastics & Statistics Seminar / Leskelä

David Adame-Carrillo

**Virasoro structure of the discrete GFF: basic techniques and some results**

Tuesday 02 May 2023, 10:15, M3 (M234)

I will discuss the basic tools of discrete complex analysis on
Z
2
that we use to construct a Virasoro representation on the space of local fields of the discrete Gaussian Free Field. I will also go over some recent results we obtained with Delara Behzad and Kalle Kytölä.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Asadollah Aghajani

**Semilinear elliptic equations with sublinear first order terms (Part 2)**

Friday 28 April 2023, 10:15, M3 (M234)

Seminar on analysis and geometry

Hannukainen, Antti (Aalto)

**TBA**

Thursday 27 April 2023, 14:15, U7

Aalto-Helsinki Applied Mathematics Seminar

Asadollah Aghajani

**Semilinear elliptic equations with sublinear first order terms (Part 1)**

Wednesday 26 April 2023, 10:15, M3 (M234)

Seminar on analysis and geometry

Sung-Chul Park (Korea Institute for Advanced Study)

**Scaling Limit of Planar Ising Model through Discrete Complex Analysis**

Tuesday 25 April 2023, 10:15, M3 (M234)

In this expository talk, I will give an outline of the developments in the field of critical and massive scaling limits in the Ising model in two dimensions starting from the breakthrough work of Smirnov, which defined the notion of s-holomorphicity. Emphasis will be placed on explaining the steps and techniques used to relate this discrete complex analytic notion to analysis in continuum, yielding conformal invariance of the model in the critical case.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Miika Hannula (University of Helsinki)

**On database dependencies and information inequalities**

Monday 24 April 2023, 15:15, M2 (M233)

In databases, notions of dependence and independence play a crucial role. For instance, every database relation typically has a key, which is a set of attributes that functionally determines the remaining attributes in the relation. By taking a uniform distribution over the database relation, these dependency notions can be recast using Shannons information measures. Consequently, logical implication between database dependencies can (sometimes) be reconceptualized as an information inequality, that is, a linear inequality over entropies. In this talk we review these connections and also consider information inequalities from a computational perspective. Unlike logical implication in database theory, not much seems to be known about the exact computational complexity of decision problems associated with information inequalities.

Algebra and discrete mathematics seminar

Pattanun Chanpiwat (University of Maryland & Aalto University)

**The policy graph decomposition of multistage stochastic programming problems**

Thursday 20 April 2023, 16:15, M203

Further information

We start at 16.00h with coffee & pulla. The talk starts at 16.15h.

Gamma-optinars - Seminars of the Group of Applied Mathematical Modelling and Optimisation (GAMMA-OPT))

Serge Kas Hanna

**Error-correcting codes for DNA storage**

Wednesday 19 April 2023, 16:15, M3 (M234)

DNA storage is a promising candidate for next-generation storage systems due to its compactness, high durability, and energy efficiency. However, the process of storing digital data in synthetic DNA suffers from deletion and insertion errors that may affect the sequence of nucleotides during synthesis, sequencing, and storage. The reliability of the DNA storage can be improved by integrating codes that correct deletions and insertions within the storage system. This talk will give a general overview of deletion/insertion correcting codes and discuss the specific encoding and decoding constraints imposed by the technologies used in DNA storage systems.

ANTA Seminar / Hollanti et al.

Konstantin Izyurov (University of Helsinki)

**BPZ equations and OPE for the critical Ising correlations.**

Tuesday 18 April 2023, 10:15, M3 (M234)

The correlation functions in conformal field theories, in particular, in minimal models, enjoy a number of properties. Among them are, in particular, Belavin-Polyakov-Zamolodchikov equations, which are second order partial differential equations, and the Operator product expansion (OPE) hypothesis concerning the asymptotic expansions of correlations to all orders.
The correlations in scaling limit of the critical the Ising model have been recently computed rigorously. However, the program of relating them on mathematical level to correlations in a minimal CFT is not completed, and deriving the BPZ equations and the OPE from the explicit expressions is not straightforward. In this talk, I will discuss our recent results in this direction. This is a joint work with Christian Webb.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Olga Kuznetsova (Aalto University)

**Weak maximum likelihood threshold of coloured Gaussian graphical models**

Monday 17 April 2023, 15:15, M2 (M233)

Colored Gaussian graphical models are linear concentration models arising from undirected graphs with a coloring in its vertices and edges. Given a coloured Gaussian graphical models, one may be interested to know how many observations are necessary for a maximum likelihood estimate to exist with positive probability. This is called the weak maximum likelihood threshold of a graph. We discuss computational and algebraic methods for studying the weak maximum likelihood threshold of a graph.

Algebra and discrete mathematics seminar

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Monday 17 April 2023, 09:30, Riihi (Y225a)

Further information

Heikki Myllykoski (FMI)

**Sparse Bayesian learning for interpolation of radar volumes**

Friday 14 April 2023, 09:15, M3 (M234)

Eetu Haavisto (SpectroCor)

**Model optimization for diffuse reflection spectroscopy**

Thursday 13 April 2023, 12:15, M203

Kash Barker, Ph.D., (University of Oklahoma, USA)

**Two-Stage Stochastic Program for Environmental Refugee Displacement Planning**

Tuesday 11 April 2023, 15:15, M1 (M232)

Forced displacement is a global problem that requires planning for the relocation and integration of displaced people. Most studies focus on conflict-driven forced displacement, and hence the refugee resettlement problem. These studies generally focus on short-term planning and assume that demand within the fixed time interval is given. However, forced displacement, including environmental displacement as well as conflict-driven displacement, is not a one-time event. On the contrary, it is an ongoing and long-term process with dynamic parameters. We are interested in the long-term displacement problem, especially for climate-driven cases in which people will be forced to leave uninhabitable regions in to escape slow-onset climate change impacts such as water stress, crop failure, and sea level rise. To reflect the long-term planning requirements of the climate-driven displacement problem in the parameters and the model, we propose a two-stage stochastic program where demand uncertainty is represented with various demand scenarios, demand and capacity are managed dynamically, and integration outcomes and related costs are optimized.

Peter Kristel (Bonn)

**Extending the free fermion Segal CFT**

Tuesday 11 April 2023, 10:15, M3 (M234)

The free fermion was one of Segal's original examples of a theory satisfying his Conformal Field Theory (CFT) axioms. This was made fully rigorous relatively recently by James Tener. I will review Segal's definition of a CFT, and then describe the free fermion. Then, I will report on some of my ongoing work attempting to extend the free fermion, following Stolz and Teichner.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Ivàn Blanco Chacón

**Twin primes in quadratic sequences and a partial answer to a conjecture by Sun**

Wednesday 05 April 2023, 15:15, M3 (M234)

The following conjecture was made in the 2016 Ireland BT Young Scientist Competition: every prime number q>3 can be expressed as q=p+n(n+1), with p a twin prime and n>0. This conjecture was satisfactorily tested for the first 100 millions of primes, and puzzled by such phenomenon, Gary McGuire asked me to think about a possible proof (or disproof) of the conjecture. The first result I came across is the proof that the validity of the conjecture would easily yield the existence of infinitely many twin primes. The conjecture remains open, but we proved that for each prime q of a set of primes of density 1, can be written as q=p+n(n+1), with p < q also prime (not necessarily twin), which is a weak version of a conjecture by Sun. In the present talk we give a sketch of this proof.

ANTA Seminar / Hollanti et al.

Yu Liu (Aalto University)

**Modeling design and control problems involving neural network surrogates**

Thursday 30 March 2023, 16:15, M203

Further information

We start at 16.00h with coffee & pulla. The talk starts at 16.15h.

Gamma-optinars - Seminars of the Group of Applied Mathematical Modelling and Optimisation (GAMMA-OPT))

Liam Hughes (University of Cambridge)

**Metric gluing of Liouville quantum gravity surfaces**

Tuesday 28 March 2023, 11:15, M3 (M234)

Introduced by Polyakov in the 1980s, Liouville quantum gravity (LQG) is in some sense the canonical model of a random fractal Riemannian surface, constructed using the Gaussian free field. Sheffield showed that when a certain type of LQG surface, called a quantum wedge, is decorated by an appropriate independent SLE curve, the wedge is cut into two independent surfaces which are themselves quantum wedges, and that these resulting wedges uniquely determine the original surface as well as the SLE interface. We prove that the original surface can in fact be obtained as a metric space quotient of the LQG metrics on the two wedges. This was proven by Gwynne and Miller in the special case $\gamma = \sqrt{8/3}$, for which $\gamma$-LQG surfaces are equivalent to Brownian surfaces, allowing an explicit description of the metric in terms of Brownian motion that is not available in general. I will explain how our work uses GFF techniques to extend their results to the whole subcritical regime $\gamma \in (0,2)$, while establishing new estimates describing the boundary behaviour of LQG. Joint work with Jason Miller.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Félix Lequen (CY Cergy Paris)

**Bourgain's construction of finitely supported measures with regular Furstenberg measure**

Tuesday 28 March 2023, 10:15, M3 (M234)

The possible asymptotic distributions of a random dynamical system are described by stationary measures, and in this talk we will be interested in the properties of these measures - in particular, whether they are absolutely continuous. First, I will quickly describe the case of Bernoulli convolutions, which can be seen as generalisations of the Cantor middle third set, and then the case of random iterations of matrices in SL(2, R) acting on the real projective line, where the stationary measure is unique under certain conditions, and is called the Furstenberg measure. It had been conjectured that the Furstenberg measure is always singular when the random walk has a finite support. There have been several counter-examples, and the aim of the talk will be to describe that of Bourgain, where the measure even has a very regular density. I will explain why the construction works for any simple Lie group, using the work of Boutonnet, Ioana, and Salehi Golsefidy on local spectral gaps in simple Lie groups.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Tobias Boege (Aalto University)

**Matroids in information theory**

Monday 27 March 2023, 15:15, M2 (M233)

Matroids capture combinatorial properties of independence in linear algebra and graph theory. It is less well-known that (poly)matroidal structures also appear as entropy functions of discrete random variables. We give an introduction to this point of view and survey relevant results and examples.

Algebra and discrete mathematics seminar

Dr. David Karpuk, WithSecure

**Recent progress in secure distributed computation**

Wednesday 22 March 2023, 16:15, M3 (M234)

In this talk we will explore some recent results in Secure Distributed Computation, in which a user distributes a computational task across several worker nodes while protecting sensitive aspects of the computation from potential adversaries with access to the worker nodes. This presentation will focus on the case of matrix multiplication, but we will discuss generalizations with potential applications to decentralized machine learning. Many of our results represent joint work with Razan Tajeddine.

ANTA Seminar

Masashi Misawa (Kumamoto University)

**Expansion of positivity and Hölder regularity for doubly nonlinear parabolic type equations**

Wednesday 22 March 2023, 12:15, M3 (M234)

Seminar on analysis and geometry

Kieran Ryan (TU Vienna)

**Fermionic and Bosonic features of the Double Dimer model and Gaussian free field**

Tuesday 21 March 2023, 10:15, M3 (M234)

The double dimer model (DDM) on a planar graph is a model of random loops, and the Gaussian free field (GFF) is a model of a height function. The two models are linked by a conjecture that the DDM loops converge in the scaling limit to loops in the continuum, which are level lines of the GFF.
I will introduce these two models and outline two results. First, certain 2n-point correlation functions in the DDM are known to be determinants in the 2-point functions; we give a new proof of this, which in particular we show can be extended to the GFF. Second, it is known that the GFF exhibits a "height gap": if one sets the boundary height to be +\lambda on one half of the boundary, and -\lambda on the other, then if \lambda = \sqrt(pi/8), the zero level line actually exhibits a sharp "jump" of 2\lambda. We give a simple derivation of this special value of the height gap, using the determinental result.
Joint work with Marcin Lis (TU Vienna)

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Nikita Belyak (Aalto University)

**Optimal Classification Trees**

Thursday 16 March 2023, 16:15, M203

Further information

We start at 16.00h with coffee & pulla. The talk starts at 16.15h.

Gamma-optinars - Seminars of the Group of Applied Mathematical Modelling and Optimisation (GAMMA-OPT))

Hiroshi Isozaki (University of Tsukuba) , Yuya Suzuki (Aalto University)

**Wave scattering in the Penrose diagram / Numerical integration and function approximation on Rd using equispaced points and lattice points**

Thursday 16 March 2023, 14:15, U7

Hiroshi Isozaki (University of Tsukuba, isozakih@math.tsukuba.ac.jp): Wave scattering in the Penrose diagram
Yuya Suzuki (Aalto University, yuya.suszuki@aalto.fi): Numerical integration and function approximation on Rd using equispaced points and lattice points

Aalto-Helsinki Applied Mathematics Seminar

Dr. Özgür Ceyhan, CritiX, University of Luxembourg

**From fault tolerance to combinatorial geometry and more**

Wednesday 15 March 2023, 16:15, M3 (M234)

Nonlinear dynamical systems pose a significant challenge when it comes to controlling them. The challenge raises to another level if we require fault tolerance. In this talk, I introduce Byzantine fault tolerance (BFT) protocols that aim at resiliency by guaranteeing consistency. I will discuss the essential combinatorial geometry behind BFT, which it shares with seemingly distant areas in math, such as Cantor's work on cardinality of reals and Turing's Halting problem. Finally, if time permits (i.e., when the eyes start rolling), I will discuss how the Diagonal Argument (from category theory) provides a unifying framework to discuss all. I assume no prior knowledge of these subjects and will try to introduce and discuss the basics.

ANTA Seminar

Anna-Mariya Otsetova (Lund University)

**Axisymmetric capillary waves on cylindrical fluid jets**

Wednesday 15 March 2023, 14:15, M203

Seminar / Tölle

Kim Myyryläinen

**Two weight norm inequalities for parabolic maximal function**

Wednesday 15 March 2023, 12:15, M3 (M234)

Seminar on analysis and geometry

Iván Blanco Chacón (University of Alcalá, Madrid )

**From Number Theory to postquantum Cryptography. Ten years (at least) of travel.**

Tuesday 14 March 2023, 15:15, U6 (U149)

Euler didn't conceive his notorious theorem as an efficient manner to cipher messages, but two centuries later, his result backs the omnipresent RSA cryptosystem. Neither Abel, nor Poincaré were specially concerned on how to communicate messages in a secure manner when they tackled elliptic integrals and still, elliptic curves are at the basis of the SSL and TLS Internet protocols.
With the frantic development of quantum computing (IBM announced Osprey three months ago, a 433 qbits processor, beating its already commercialised 21 qbits QSystem1 ), we must set ourselves en guard as soon as possible. This is the reason why the NIST launched a public contest to standardise postquantum cryptographic primitives in 2017, recently resolved in July 2022. However, the mathematical tools backing these new proposals are, if no more complicated, at least more challenging than the previous ones.
The goal of my talk is to mention my research lines developed since 2011 until now, a journey which started in Barcelona with such ethereal topics as Shimura curves, modularity and p-adic L-functions and led me to questions as designing efficient codes, crypto-analysing postquantum primitives while still working in more mystic maths in my free time.

Riina Hakkarainen

**Drift detection methods for data streams**

Tuesday 14 March 2023, 12:15, M3 (M234)

Ethan Sussman (MIT)

**Towards a rigorous Coulomb-gas formalism for the minimal models (contd.)**

Tuesday 14 March 2023, 10:15, M3 (M234)

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Dissertation

Topi Kuutela. Opponent: Bastian von Harrach (Goethe University Frankfurt)

**Computational and theoretical models in diffuse imaging**

Friday 10 March 2023, 12:00, A2

Ethan Sussman (MIT)

**Towards a rigorous Coulomb-gas formalism for the minimal models, part 2**

Thursday 09 March 2023, 10:15, Y307

In the late 80's, the physicists Dotsenko and Fateev used the Coulomb-gas formalism to solve for the structure constants of Belavin--Polyakov--Zamolodchikov's minimal models of 2D CFT. To this day, their analysis has not been made mathematically rigorous. In this talk, we will discuss progress towards a rigorous Coulomb-gas formalism, along with its application to the construction of the minimal models.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Timo Takala

**Vanishing subspaces of the John-Nirenberg space**

Wednesday 08 March 2023, 12:15, M3 (M234)

Seminar on analysis and geometry

Ethan Sussman (MIT)

**Towards a rigorous Coulomb-gas formalism for the minimal models**

Tuesday 07 March 2023, 11:15, M3 (M234)

In the late 80's, the physicists Dotsenko and Fateev used the Coulomb-gas formalism to solve for the structure constants of Belavin--Polyakov--Zamolodchikov's minimal models of 2D CFT. To this day, their analysis has not been made mathematically rigorous. In this talk, we will discuss progress towards a rigorous Coulomb-gas formalism, along with its application to the construction of the minimal models.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Stephen Moore (Institute of Mathematics Polish Academy of Sciences)

**Limits of traces for Temperley-Lieb algebras**

Tuesday 07 March 2023, 10:15, M3 (M234)

In recent decades, there have been interesting connections made between a number of areas of mathematics, including statistical mechanics, knot theory, quantum groups, and subfactors. The Temperley-Lieb algebras are a family of finite dimensional algebras that were the original source of these connections. In this talk we review the representation theory of the finite Temperley-Lieb algebras. We then discuss extremal traces, their classification, and applications to the representation theory of an infinite dimensional generalization of the Temperley-Lieb algebra.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Ethan Sussman (MIT)

**Towards a rigorous Coulomb-gas formalism for the minimal models.**

Tuesday 07 March 2023, 10:00,

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Monday 06 March 2023, 09:30, Riihi (Y225a)

Further information

Joonatan Bergholm

**Gauss-Newton menetelmä (Kandiesitelmä)**

Friday 03 March 2023, 10:15, M2 (M233)

Paula Weller (Aalto University)

**Finite Adaptability in Multistage Linear Optimization**

Thursday 02 March 2023, 16:15, M203

Further information

We start at 16.00h with coffee & pulla. The talk starts at 16.15h.

Gamma-optinars - Seminars on the Group of Applied Mathematical Modelling and Optimisation (GAMMA-OPT))

Lauri Särkiö

**Lipschitz truncation for parabolic double phase equations**

Wednesday 01 March 2023, 12:15, M3 (M234)

Seminar on analysis and geometry

Xavier Poncini (University of Queensland)

**A planar-algebraic universe**

Tuesday 28 February 2023, 10:15, M3 (M234)

Conformal nets provide a rigorous mathematical framework for conformal field theory, assigning an algebra of observables to each region of the underlying spacetime manifold. Here, we consider so-called discrete conformal nets whereby the spacetime is not a smooth manifold but instead has an 'atomic' structure. It turns out that planar algebras can be used to construct 'almost' examples of discrete conformal nets. In this talk, I will review this business and detail recent efforts to construct fully-fledged examples of discrete conformal nets. Inspired by the statistical mechanics literature, I will also introduce some integrable operators that act on the spacetime and detail some of their algebraic structure.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Panu Lahti (Chinese Academy of Sciences)

**Alberti's rank one theorem and quasiconformal mappings in metric measure spaces**

Wednesday 22 February 2023, 12:15, M3 (M234)

We investigate a version of Albertis rank one theorem in Ahlfors regular
metric spaces, as well as a connection with quasiconformal mappings. More precisely, we give a proof of the rank one theorem that partially follows along the usual steps, but the most crucial step consists in showing for a BV mapping f that at |Df|^s-a.e. point in X, the mapping f behaves non-quasiconformally.

Seminar on analysis and geometry

Janne Junnila (University of Helsinki)

**Decompositions of log-correlated Gaussian fields**

Tuesday 21 February 2023, 10:15, M3 (M234)

Log-correlated Gaussian fields such as the Gaussian free field are random Schwartz distributions whose covariances have a logarithmic singularity on their diagonal. They appear for instance in Liouville quantum gravity, characteristic polynomials of random matrices, the dimer model etc. In this talk I will present ways to decompose general log-correlated fields into a sum of a canonical log-correlated field with a particularly nice covariance structure and a Hölder-continuous error term. I will also discuss applications to the study of the Gaussian multiplicative chaos of the field. The talk is based on joint works with Eero Saksman and Christian Webb as well as Juhan Aru and Antoine Jego.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Tomas Eklund

**Impact of air passengers on COVID-19 transmission (MSc presentation)**

Friday 17 February 2023, 14:15, M3 (M234)

Video stream at https://aalto.zoom.us/j/65615277822

MSc presentation / Lasse Leskelä

Fausto Barbero (University of Helsinki)

**Expressivity of languages for probabilistic causal reasoning**

Friday 17 February 2023, 13:00, Y229c

Causal reasoning, as developed e.g. in the works of J. Pearl and of Spirtes, Glymour & Scheines, is a collection of effective but rather disorganized mathematical techniques and ad hoc formalisms. With Gabriel Sandu, we proposed a semantic framework (causal multiteam semantics) by means of which many of the statements typical of causal reasoning (concerning e.g. conditional probabilities, "do expressions", Pearl's "counterfactuals") can be decomposed into three simpler elements: (marginal) probability statements, and two distinct conditionals, which describe the effects, respectively, of an action and of an increase in information.
In this talk I will present part of a joint work with Jonni Virtema. We gave abstract characterizations of the expressive power of a number of candidate languages for probabilistic causal reasoning; these characterizations involve identifying three special classes of linear inequalities.
By analyzing the geometry of these inequalities as interpreted in standard n-simplexes, we used the characterization results to prove that the languages form a proper hierarchy (i.e., that distinct levels of generality of the syntax correspond to distinct levels of expressivity) and to prove some further undefinability result.

Algebra and Discrete Mathematics Seminar (Boege, Orlich)

Prof. Anita Schöbel (RPTU Kaiserslautern and Fraunhofer ITWM)

**Robust multi-objective optimization**

Tuesday 14 February 2023, 15:15, U6 (U149)

Most real-world optimization problems contain parameters which are not known at the time a decision is to be made. In robust optimization one specifies the uncertainty in a scenario set and tries to hedge against the worst case.
Classical robust optimization aims at finding a solution which is best in the worst-case scenario. It is a well-studied concept but it is known to be very conservative: A robust solution comes with a high price in its nominal objective function value. This motivated researchers to introduce less conservative robustness concepts in the last decade. Moreover, many real-world problems involve not only one, but multiple criteria. While robust single-objective optimization has been investigated for 25 years, robust multi-objective optimization is a new field in which already the definition of "robust" is a challenge.
In the talk, several robustness concepts will be discussed and
illustrated at applications from public transport.

**Eemil Halonen (Matematiikan kandidaattiseminaari )**

Friday 10 February 2023, 09:00, M3 (M234)

Further information

Performance comparison of 3D wind Anemometers

Prof. William Mance, University of Adam Mickiewicz in Poznan

**Normal numbers**

Wednesday 08 February 2023, 16:15, M3 (M234)

Informally, a real number is normal in base b if in its b-ary expansion all digits and blocks of digits occur as often as one would expect them to uniformly at random. Borel introduced normal numbers in 1909 and proved that Lebesgue-almost every real number is normal in all bases b \geq 2. Even though this shows that, in some sense, normal numbers are "typical," no example of a number normal in all bases was given until 1939 by Turing. In the last 100 years, the study of normal numbers has spread over a wide breadth of seemingly unrelated disciplines. Normality is closely related to number theory, ergodic theory, theoretical computer science, probability theory, fractal geometry, descriptive set theory, and others areas of math. We will explore the basic properties of normal numbers and surprising connections they have, depending on the interest of the audience.

ANTA Seminar

Wontae Kim

**Whitney decomposition for the parabolic double phase problem**

Wednesday 08 February 2023, 12:15, M3 (M234)

Seminar on analysis and geometry

Sándor Kisfaludi-Bak (Aalto)

**On geometric variants of the traveling salesman problem**

Tuesday 07 February 2023, 14:00, M237

In the classic Euclidean traveling salesman problem, we are given n points in the Euclidean plane, and the goal is to find the shortest round trip that visits all the points. We will briefly discuss how modern algorithmic and lower bound tools allowed us to find (conditionally) optimal exact and approximation algorithms for this problem, while the closely related Steiner tree problem seems to resist many similar attempts. We will then turn to the traveling salesman or Steiner tree with "neighborhoods". Here instead of points, we are given a set of affine subspaces, and the goal is to find the shortest round trip or tree that intersects each subspace. It turns out that these problems have a different computational complexity than the classic problems with points: they require a completely novel approach for the hyperplane case, while the other cases remain largely mysterious.

Algebra and Discrete Mathematics Seminar (Boege, Orlich)

Petri Laarne (University of Helsinki)

**Almost sure solution of nonlinear wave equation: from donut to plane**

Tuesday 07 February 2023, 10:15, M2 (M233)

I discuss the recent preprint [arXiv:2211.16111] of Nikolay Barashkov and I, where we show the almost sure well-posedness of a deterministic nonlinear wave equation (cubic Klein-Gordon equation) on the plane. Here "almost sur" is in respect to the \\\\phi^4 quantum field theory. I briefly introduce the invariant measure argument and outline the solution on 2D torus due to Oh and Thomann. I then explain our main contributions: extension of periodic solutions to infinite volume, and a weaker result for nonlinear Schrödinger equation. The viewpoint is functional-analytic with a dash of probability.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Rahinatou Yuh Njah

**Ring/Polynomial learning with errors (RLWE/PLWE): Equivalence and attacks**

Wednesday 01 February 2023, 16:15, M3 (M234)

ANTA Seminar

Asadollah Aghajani

**Regularity of stable solutions to elliptic PDEs and Gelfand-type problems II**

Wednesday 01 February 2023, 12:15, M3 (M234)

Seminar on analysis and geometry

Tuomas Kelomäki

**Using discrete Morse theory algebraically Part 2**

Tuesday 31 January 2023, 14:00, M237

Algebra and discrete mathematics seminar

Kalle Koskinen (University of Helsinki)

**Infinite volume states of the mean-field spherical model in a random external field**

Tuesday 31 January 2023, 10:15, M2 (M233)

One method of introducing external randomness to a Gibbs state, as opposed to the internal randomness of the Gibbs state itself, is to perturb the Hamiltonian with a term corresponding to the coupling of a random external field to the system. For the mean-field spherical model, the corresponding perturbed model can be exactly solved, in some sense, in the infinite volume limit. In this talk, we will introduce, motivate, and present some constructions and results concerning the so-called infinite volume metastases of the mean-field spherical model in a random external field. The aim of this talk is to present the general theory of disordered systems as it pertains to this particular model, and highlight the particular aspects of this model which lead to its curious behaviour as a disordered system. This talk is based on work in a recently accepted paper to appear in the Journal of Statistical Physics.

Aalto mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Petri Laarne (University of Helsinki)

**Almost sure solution of nonlinear wave equation: from donut to plane**

Wednesday 25 January 2023, 20:19, M2 (M233)

Prof. Alexandru Paler

**Graph states and the challenges for efficient quantum circuit compilation**

Wednesday 25 January 2023, 16:15, M3 (M234)

Graphs can be used as a diagrammatic representation of entangled states: vertices represent qubits, and edges are the entangling gates performed between the qubits. Arbitrary quantum circuits can be compiled into a fault-tolerant gate set, and the resulting circuit can be reformulated as a graph state. Such graphs can be manipulated by local operations (single qubit/vertex gates) such that edges are added and removed in a well defined manner during a process called local complementation. The latter might have interesting applications for the optimisation of (fault-tolerant) quantum circuits, quantum communication networks and in general whenever, either: a) there is a need to minimize the number of edges (entangling gates) without affecting the functionality of the state, or b) the state has to be embedded into a quantum hardware architecture that has a different connectivity. This talk is partially based on the work from https://arxiv.org/abs/2209.07345

ANTA Seminar

Asadollah Aghajani

**Regularity of stable solutions to elliptic PDEs and Gelfand-type problems I**

Wednesday 25 January 2023, 12:15, M3 (M234)

Seminar on analysis and geometry

Tuomas Kelomäki

**Using discrete Morse theory algebraically**

Tuesday 24 January 2023, 14:00, M237

This is an introductory talk on discrete Morse theory and especially on Sköldberg's algebraic formulation of it. The goal is to learn the method through several examples. If the time permits, we will also derive finite versions of several classical results in homological algebra from the theory.

Algebra and Discrete Mathematics Seminar (Boege, Orlich)

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Friday 20 January 2023, 09:30, Riihi (Y225a)

Further information

Wilmar Bolanos

**The trace form over cyclic number fields**

Wednesday 18 January 2023, 16:15, M3 (M234)

For a given number field K, the integral trace form of K is the quadratic form defined by the trace operator Tr_K/Q(x^2) over the ring of integers of K. In the mid 80's Conner and Perlis showed that for cyclic number fields of prime degree p the isometry class of integral trace is completely determined by the discriminant. The main objective of this talk is to discuss the principal aspects of Conner and Perlis' work and a completed generalization for tame cyclic number fields of arbitrary degree. Furthermore, for such fields, we give an explicit description of a Gram matrix of the integral trace in terms of the discriminant of the field.

ANTA Seminar

Tuomas Sahlsten

**PDEs and dynamics**

Wednesday 18 January 2023, 12:15, M3 (M234)

In these talks we will discuss various methods how the theory of dynamical systems can be used to study PDEs such as wave- or Schrödinger equation on planar domains or manifolds. The talks are more an introduction to the ideas, and we try not to assume any background knowledge on the concepts discussed. In the first talk we will focus on 2D surfaces without boundary, where the dynamics is given by the geodesic flow. Here a pre-trace formula due to Selberg allows us to connect eigenfunctions of the Laplacian and the lengths of the periodic orbits of the dynamics. We then outline how number theoretic assumptions on the surface or randomly sampling the surfaces helps to control the complicated periodic orbit structure.

Seminar on analysis and geometry

Camilla Hollanti

**Capacity of private information retrieval from coded and colluding servers (online talk at the Technion Coding Theory Seminar) **

Wednesday 11 January 2023, 16:30, Zoom

Further information

Private information retrieval (PIR) addresses the question of how to retrieve data items from a database or cloud without disclosing information about the identity of the data items retrieved. The area has received renewed attention in the context of PIR from coded storage. Here, the files are distributed over the servers according to a storage code instead of mere replication. Alongside with the basic principles of PIR, we will review recent capacity results and demonstrate the usefulness of the so-called star product PIR scheme.
The talk is based on joint work with Ragnar Freij-Hollanti, Oliver Gnilke, Lukas Holzbaur, David Karpuk, and Jie Li.

Technion Coding Theory Seminar/ANTA Seminar

René Langøen (University of Bergen)

**The direct monodromy problem and isomonodromic deformations for the Rabi model**

Tuesday 10 January 2023, 10:15, M2 (M233)

We discuss the local and global solutions of the Rabi model in Garnier form, a linear system of first order differential equations, with complex rational coefficients. The analytic continuation of the local solutions are described by a monodromy group, which gives a matrix representation of the fundamental group of the punctured Riemann sphere. A detailed geometric description of linear systems of first order differential equations is given, in terms of a local family of connection forms on a principal bundle. The geometric description reveals the Frobenius integrability conditions, which are used to obtain necessary and sufficient conditions for an isomonodromic deformation of the Rabi model.

mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Emil Verkama

**Repairing the universality theorem for 4-polytopes**

Monday 09 January 2023, 11:00, M2 (M233)

Master's thesis presentation

Jarno Maaninen

**Bayesian experimental design for magnetorelaxometry imaging**

Thursday 05 January 2023, 11:00, M3 (M234)

Master's thesis presentation

Saara Vestola

**Enhancement of data veracity for preamble signature ID classification in PRACH, Master thesis talk **

Tuesday 20 December 2022, 11:00, M237

Oscar Kivinen (EPFL, Lausanne)

**Plane curves: a bridge between number theory, knots, and physics**

Friday 16 December 2022, 15:30, M237

Plane curves are some of the simplest classical algebro-geometric objects, that most of us encounter in middle school (over the real numbers). Especially their singularity theory remains a source of many interesting discoveries. For example, it turns out many moduli spaces of sheaves on singular plane curves are related to 1) arithmetic problems arising in the Langlands program 2) physics of some 3d/4d supersymmetric gauge theories.
On the other hand, in most cases a lot of data about the singularities is controlled by the knots arising as their links, and one may ask how the relevant knot theory is reflected in the themes 1) and 2) above. I will give an introduction to plane curves and discuss the relation to 1) and possibly 2), highlighting a recent result about "orbital integrals on p-adic groups (obtained by myself and Tsai) where the topology of the singularities informs the arithmetic. Little background knowledge will be required, apart from knowing what knots, finite fields, and the general linear group are.

Algebra and Discrete Mathematics Seminar

Toni Annala (Institute for Advanced Study)

**Topologically protected tricolorings**

Friday 16 December 2022, 14:00, M237

Topological vortices are codimension-one topological defects that arise in various physical systems, such as liquid crystals, Bose--Einstein condensates, and vacuum structures of Yang--Mills theories. I will explain how, under certain homotopical assumptions that are satisfied in many realistic systems, topological vortex configurations admit faithful presentations in terms of colored link diagrams. The most well-known coloring scheme of links is given by tricolorings: each arc of the link diagram is colored by one of three possible colors (red, green, or blue) in such a way that, in each crossing, either all arcs have the same color, or all arcs have a different color. A tricolored link is topologically protected if it cannot be transformed into a disjoint union of unlinked simple loops by a sequence of color-respecting isotopies and color-respecting local cut-and-paste operations. The latter operations are referred to as allowed local surgeries. We use equivariant bordism groups of three-manifolds to construct invariants of colored links that are conserved in allowed local surgeries, and employ the invariant to classify all tricolored links up to local surgeries. The talk is based on joint work with Hermanni Rajamäki, Roberto Zamora Zamora, and Mikko Möttönen.

Algebra and Discrete Mathematics Seminar

Tuomas Tuukkanen (Princeton & Aalto)

**Fermionic Fock Spaces in Conformal Field Theory (MSc thesis presentation)**

Friday 16 December 2022, 11:00, M3 (M234)

mathematical physics seminar (Kytölä / Peltola / Sahlsten)

Vivian Healey (Texas State University)

**Loewner evolution, Dyson Brownian motion, and tree embeddings**

Thursday 15 December 2022, 10:15, M3 (M234)

The Loewner equation gives a correspondence between curves in the upper half-plane (or disk) and continuous real functions (called the driving function for the equation). When the driving function is Brownian motion, the result is Schramm-Loewner Evolution (SLE). In this talk, we will discuss links between multiple Loewner evolution and Dyson Brownian motion. First, we show that multiple radial SLE is generated by Dyson Brownian motion on the circle. Second, we show that in the chordal case, scaling the Brownian term to 0 in a branching Dyson Brownian motion generates tree embeddings in the halfplane. If time allows, we will also discuss the Dyson superprocess, which is the scaling limit of this driving measure when the branching structure is conditioned to converge to the continuum random tree. (Joint work with Gregory Lawler and Govind Menon)

mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Anne Schreuder (Cambridge University)

**On Lévy-driven Loewner Evolutions **

Thursday 08 December 2022, 10:15, Y405

This talk is about the behaviour of Loewner evolutions driven by a Lévy process. Schramm's celebrated version (Schramm-Loewner evolution), driven by standard Brownian motion, has been a great success for describing critical interfaces in statistical physics. Loewner evolutions with other random drivers have been proposed, for instance, as candidates for finding extremal multifractal spectra, and some tree-like growth processes in statistical physics. Questions on how the Loewner trace behaves, e.g., whether it is generated by a (discontinuous) curve, whether it is locally connected, tree-like, or forest-like, have been partially answered in the symmetric alpha-stable case. We consider the case of general Levy drivers. Joint work with Eveliina Peltola (Aalto and Bonn).

mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Delara Behzad (Aalto University)

**On Schubert derivation and applications**

Thursday 01 December 2022, 10:15, Y405

mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Okko Makkonen

**Complexity of matrix multiplication**

Wednesday 30 November 2022, 16:15, M3 (M234)

The complexity of matrix multiplication represents the number of operations needed to compute a matrix product in the asymptotic limit. The first advance in asymptotic complexity was made in 1969 when Strassen introduced an algorithm that is capable of computing the product of two N × N matrices with O(N^{2.81}) operations, which is better than the naive algorithm that takes O(N^3) operations. The current record is an algorithm that is able to compute the product using just O(N^{2.372}) operations. We present the basic tools that are used to analyze this problem and present an algorithm that is even better than the Strassen algorithm. This includes studying the matrix multiplication tensor, its rank, and the so-called border rank.

ANTA Seminar

Lauri Särkiö

**Parabolic Lipschitz truncation**

Wednesday 30 November 2022, 12:15, M3 (M234)

Seminar on analysis and geometry

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Wednesday 30 November 2022, 09:30, Riihi (Y225a)

Further information

Dissertation

DI, VTM Emma-Karoliina Kurki

**Weight theory on bounded domains and metric measure spaces**

Friday 25 November 2022, 12:00, M1 (M232)

ForAlli

**Ad hoc formalization (ForAlli monthly special)**

Thursday 24 November 2022, 16:15, M2 (M233)

ForAlli

Delara Behzad (Aalto University)

**On Schubert derivation and applications**

Thursday 24 November 2022, 10:15, Y405

mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Sheldy Ombrosi

**Theory of weights in regular trees**

Wednesday 23 November 2022, 12:15, M3 (M234)

Seminar on analysis and geometry

Olli Huopio

**Master Thesis Talk : A sensor fusion algorithm for land vehicle positioning**

Monday 21 November 2022, 14:00, Riihi (Y225a)

Alex Karrila (Åbo Akademi)

**The phases of random Lipschitz functions on the honeycomb lattice**

Monday 21 November 2022, 11:00, Y229a

stochastics and mathematical physics seminar (Kytölä, Leskelä, Peltola)

Teemu Lundström

**Yamada Polynomials from Transfer-Matrix Methods**

Friday 18 November 2022, 14:15, M237

Spatial graphs are graphs that are embedded in three-dimensional space. They are in some sense a generalization of knots and the theory of spatial graphs is closely related to knot theory. In knot theory, one can distinguish between two inequivalent knots by computing some algebraic invartiant of them, for example, the Jones polynomial. Similar invariants have been invented for spatial graphs and one important such invariant is the Yamada Polynomial, first introduced by Shuji Yamada in 1989. In this talk I will introduce spatial graphs and the Yamada polynomial defined for them. I will focus on computing the polynomial for certain classes of graphs that have a layer-like structure. Computing the Yamada polynomial for a spatial graph can be computationally demanding, but by focusing on such graphs we are able to apply the so called transfer-matrix method with which we are able to find a closed form formula for two infinite families of spatial graphs.

Algebra and Discrete Mathematics Seminar

Johan Lindell (first speaker), Salla Tanskanen (second speaker), Matias Koponen (third speaker, topic presentation)

**Bachelor's thesis presentations**

Wednesday 16 November 2022, 15:15, M2 (M233)

Further information

Kim Myyryläinen

**A weighted fractional Poincare inequality, Part 2**

Wednesday 16 November 2022, 12:15, M3 (M234)

Seminar on analysis and geometry

Pengmin Hua (PhD midterm review talk)

**Optimal control of indoor thermal comfort based on district heating with thermal energy storage**

Monday 14 November 2022, 11:00, Y229c

PhD midterm review talks

Kirthivaasan Puniamurthy (PhD midterm review talk)

**On proving adaptive security for Yao's garbling scheme**

Monday 14 November 2022, 10:00, Y229c

PhD midterm review talks

Niklas Miller (PhD midterm review talk)

**Lattice point enumeration and wiretap decoding probability estimates**

Monday 14 November 2022, 09:00, Y229c

PhD midterm review talks

Paul Van Dooren

**Social Balance, Gossiping and Riccati Equations**

Friday 11 November 2022, 13:30, M203

Social networks with positive and negative links often split into two antagonistic factions. Examples of such a split abound: revolutionaries versus an old regime, Republicans versus Democrats, Axis versus Allies during the second world war, or the Western versus the Eastern bloc during the Cold War. Although this structure, known as social balance, is well understood, it is not clear how such
factions emerge. An earlier model could explain the formation of such factions if reputations were assumed to be symmetric. We show this is not the case for non-symmetric reputations, and propose an alternative model which (almost) always leads to social balance, thereby explaining the tendency of social networks to split into
two factions. In addition, the alternative model may lead to cooperation when faced with defectors, contrary to the earlier model. The difference between the two models may be understood in terms of
the underlying gossiping mechanism: whereas the earlier model assumed that an individual adjusts his opinion about somebody by gossiping about that person with everybody in the network, we assume instead that the individual gossips with that person about everybody. It turns out that the alternative model is able to lead to cooperative behavior, unlike the previous model.

Osama Abuzaid (PhD midterm review talk)

**On self avoiding random walks and Schramm Loewner evolutions**

Thursday 10 November 2022, 13:00, M2 (M233)

PhD midterm review talks

Serge Kas Hanna

**Introduction to federated learning**

Wednesday 09 November 2022, 16:15, M3 (M234)

Distributed learning (DL) is a machine learning (ML) setting where several parties (e.g., mobile devices or computer clusters) collaboratively train an ML model under the orchestration of a central entity. DL can be applied in the case where the data is centralized, i.e., owned by a single entity, and also when the data is decentralized, i.e., owned by several parties. In the centralized data setting, DL is attractive when the data is too large for one entity to process by itself. Here, a central entity can make the learning process tractable by distributing the data across several helper nodes and outsourcing part of the computations. The DL setting can also present itself naturally when the training data is owned by several decentralized parties.
Federated learning (FL) is a branch of DL where the data is decentralized and owned by several independent parties who agree to collaboratively train an ML model but want to maintain the privacy of their local data. In addition to privacy, communication efficiency is also a first-order concern in FL, especially when the data is owned by several mobile devices operating over a network.
In this talk, I will introduce distributed learning and federated learning and discuss some of the challenges associated with such distributed systems. I will also explain how basic optimization algorithms, such as gradient descent, can be applied to distributed learning and adapted to the setting of federated learning.

ANTA Seminar

Muhammad Ardiyansyah (Aalto University)

**Dimensions of the factor analysis model and its higher order generalizations**

Wednesday 09 November 2022, 15:00, M2 (M233)

The factor analysis model is a statistical model where a certain number of hidden random variables, called factors, affect linearly the behaviour of another set of observed random variables, with additional random noise. The main assumption of the model is that the factors and the noise are Gaussian random variables. In this talk, we do not assume that the factors and the noise are Gaussian, hence the higher order moment and cumulant tensors of the observed variables are generally nonzero. This motivates the generalized notion of kth-order factor analysis model, that is the family of all random vectors in a factor analysis model where the factors and the noise have finite and possibly nonzero moment and cumulant tensors up to order k. This subset may be described as the image of a polynomial map onto a Cartesian product of symmetric tensor spaces. We provide its dimension and conditions under which the image has positive codimension. This talk is based on joint work with Luca Sodomaco.

Algebra and Discrete Mathematics Seminar

Kim Myyryläinen

**A weighted fractional Poincare inequality, Part 1**

Wednesday 09 November 2022, 12:15, M3 (M234)

Seminar on analysis and geometry

talk canceled / rescheduled to a later time

**talk canceled / rescheduled to a later time**

Thursday 03 November 2022, 10:15,

mathematical physics seminar (Kytölä, Peltola, Sahlsten)

Wontae Kim

**Existence theory for the parabolic double phase problem**

Wednesday 02 November 2022, 12:15, M3 (M234)

The classical approach in existence theory does not give the existence and uniqueness of the weak solution to this problem since the function space for the gradient of weak solutions involves the time variable. We discuss the recent approach to the existence theories and how the regularity results are able to be applied to the existence theory.

Seminar on analysis and geometry

ForAlli

**Views on formalization of mathematics**

Thursday 27 October 2022, 16:15, M2 (M233)

We will watch the recordings from Microsoft Research Summit session "Empowering mathematicians with technology" (provided they are available).

ForAlli

Ellen Powell (Durham University)

**Characterising the Gaussian free field**

Thursday 27 October 2022, 10:15, Y405

I will discuss recent approaches to characterising the Gaussian free field in the plane, and in higher dimensions. The talk will be based on joint work with Juhan Aru, Nathanael Berestycki, and Gourab Ray.

mathematical physics seminar (Kytölä, Peltola, Sahlsten)

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Thursday 27 October 2022, 09:30, Riihi (Y225a)

Further information

Tapani Matala-aho

**A criterion for irrationality**

Wednesday 26 October 2022, 16:15, M3 (M234)

Take your favorite real or p-adic number, say Phi. Let us assume there exist nice rational approximations for your number. Then these approximations will be written as numerical linear forms. We will give a criterion for the irrationality of your number by using a sequence of these numerical linear forms. Moreover, a lower bound is given for the quantity N*Phi-M, where N, M are integers and N is nonzero. However, it is a challenge to find an appropriate sequence of numerical linear forms for an arbitrary number. In this lecture we will not consider this problem. But we note, if your number is a value of a Taylor series or a (generalized) continued fraction, then we may build a candidate sequence from the truncated series or Padé approximations or use the convergents of the continued fraction.

ANTA Seminar

Asadollah Aghajani

**Liouville type results for quasilininear elliptic equations with gradient dependence**

Wednesday 26 October 2022, 12:15, M3 (M234)

Seminar on analysis and geometry

Lisa Nicklasson (Università di Genova)

**Ideals arising from Bayesian networks**

Thursday 20 October 2022, 11:15, Zoom

Further information

A Bayesian network is a statistical model which can be presented graphically by a directed acyclic graph. The nodes in the graph are discrete random variables, and the edges encode dependencies between the variables. Bayesian nets can also be described algebraically as varieties of homogeneous prime ideals. In this talk we will discuss connections between algebraic properties of such ideals and combinatorial properties of the graphs. In particular, we would like to understand when the variety is toric and when the ideal is quadratic.

Algebra and Discrete Mathematics Seminar

Caroline Wormell (Sorbonne, Paris)

**Decay of correlations for conditional measures and some applications**

Thursday 20 October 2022, 10:15, Y228b

The forward evolution of chaotic systems notoriously washes out inexact information about their state. When advected by a chaotic system, physically relevant measures therefore often converge to some reference measure, usually the SRB measures. This property implies various important statistical behaviours of chaotic systems.
In this talk we discuss the behaviour of slices of these physical measures along smooth submanifolds that are reasonably generic (e.g. not stable or unstable manifolds). We give evidence that such conditional measures also have exponential convergence back to the full SRB measures, even though they lack the regularity usually required for this to occur (for example, they may be Cantor measures). Using Fourier dimension results, we will prove that CDoC holds in a class of generalised baker's maps, and we will give rigorous numerical evidence in its favour for some non-Markovian piecewise hyperbolic maps. CDoC naturally encodes the idea of long-term forecasting of systems using perfect partial observations, and appears key to a rigorous understanding of the emergence of linear response in high-dimensional systems.

Mathematical physics seminar

Emanuel Carneiro (ICTP Trieste)

**On sign Fourier uncertainty**

Wednesday 19 October 2022, 12:15, M3 (M234)

The quest to find the sharp forms of functional inequalities has always been a beautiful and challenging theme in analysis. In this talk we will discuss a few sharp inequalities related to Fourier uncertainty principles. We address the problem of prescribing the sign of a function and its Fourier transform at infinity, and doing this in an optimal way (in an appropriate sense). This phenomenon was introduced by Bourgain, Kahane and Clozel in 2010 under the name of "sign Fourier uncertainty", and brings interesting connections to the sphere packing problem.

Seminar on analysis and geometry

Gregory Arone (Stockholm University)

**The S_n-equivariant topology of partition complexes**

Thursday 13 October 2022, 11:15, M2 (M233)

Let n be a positive integer. Consider the poset of partitions of the set {1, ... , n}, ordered by refinement. Its geometric realization is a topological space that encodes information about the combinatorial properties of the partition poset. We obtain a sequence of spaces T_1, T_2, ..., T_n, ...,. In fact it is a symmetric sequence of spaces, by which we mean that the n-th space T_n has a natural action of the symmetric group S_n.
These spaces have many interesting properties, and they arise in a number of places in mathematics, from the study of Lie algebras to algebraic topology to mathematical biology. We will survey some of the properties and applications of the spaces T_1, ..., T_n,..., focusing on the properties of the action of the symmetric groups. In particular, we will give a "branching rule" that describes the restriction of T_n to a Young subgroup of S_n (this is joint work with Lukas Brantner). The proof uses discrete Morse theory, and it generalizes many previous results. I will show some applications and some open questions.

Algebra and Discrete Mathematics Seminar

Augustin Lafay (Aalto)

**Geometrical lattice models, algebraic spiders and applications to random geometry**

Thursday 13 October 2022, 11:00, Y228b

mathematical physics seminar (Kytölä / Peltola / Sahlsten)

Milo Orlich (Aalto)

**Asymptotic results on Betti numbers of edge ideals of graphs via critical graphs**

Thursday 06 October 2022, 11:15, M2 (M233)

To any graph G one can associate its edge ideal. One of the most famous results in combinatorial commutative algebra, Hochster's formula, describes the Betti numbers of the edge ideal in terms of combinatorial information on the graph G. More explicitly, each specific Betti number is given in terms of the presence of certain induced subgraphs in G. The machinery of critical graphs, relatively recently introduced by Balogh and Butterfield, deals with characterizing asymptotically the structure of graphs based on their induced subgraphs. In a joint work with Alexander Engström, we apply these techniques to Betti numbers and regularity of edge ideals. We introduce parabolic Betti numbers, which constitute a non-trivial portion of the Betti table. Usually, the vanishing of a Betti number has little impact on the rest of the Betti table. I this talk I will describe our main results, which show that on the other hand the vanishing of a parabolic Betti number determines asymptotically the structure and regularity of the graphs with that Betti number equal to zero.

Algebra and Discrete Mathematics Seminar

Mikhail Basok (University of Helsinki)

**Dimer model on Riemann surfaces and compactified free field**

Thursday 06 October 2022, 11:00, Y228b

We consider a random height function associated with the dimer model on a graph embedded into a Riemann surface. Given a sequence of such graphs approximating the surface in a certain sense we prove that the corresponding sequence of height functions converges to the compactified free field on the surface. To establish this result we follow approach developed by Dubédat: we introduce a family of observables of the model which can be expressed as determinants of discrete perturbed Cauchy-Riemann operators, we analyze the latter using Quillen curvature formula.

mathematical physics seminar (Kytölä / Peltola / Sahlsten)

Ragnar Freij-Hollanti

**Combinatorial derived matroids**

Wednesday 05 October 2022, 16:15, M3 (M234)

Let M be an arbitrary matroid. In the 70's, Gian-Carlo Rota and Henry Crapo asked for a natural definition of a matroid dM that has as its ground set the collection of (co)circuits of M. We will first survey two earlier such constructions, namely the Exley-Wang derived matroid, and (co)-adjoint lattices. These constructions have several nice properties, but are only defined for certain special classes of matroids, and are not necessarily unique. We will then introduce a recent construction by the speaker, called combinatorial derived matroids. These are uniquely defined for any matroid M, but computing them has proven an elusive task. We will give all the definitions, compute some illuminating examples, and offer a few conjectures. This is joint work with Relinde Jurrius and Olga Kuznetsova.

ANTA Seminar

Mohamed Serry (University of Waterloo)

**Physics of phonation offset: towards understanding relative fundamental frequency observations**

Thursday 29 September 2022, 13:15, M2 (M233)

Relative fundamental frequency (RFF) is a promising assessment technique for vocal pathologies. Herein, we explore the underlying laryngeal factors dictating RFF behaviors during phonation offset. To gain physical insights, we investigate a simple analytical impact
oscillator model and follow that with a numerical study using the well-established bodycover model of the vocal folds (VFs). Study of the impact oscillator suggests that the observed decrease in fundamental frequency during offset is due, at least in part, to the decrease in collision forces during abduction. Moreover, the impact oscillator elucidates a correlation between sharper drops in RFF and increased stiffness of the VFs, supporting experimental RFF studies. The body-cover model study further emphasizes the correlation between the drops in RFF and collision forces and displays the potential role of the cricothyroid muscle to mitigate the RFF reduction.

Applied Mathematics / David Radnell

Tobias Boege (Aalto University)

**Ingleton's inequality for entropies**

Wednesday 28 September 2022, 14:00, Y307

The Ingleton inequality is a necessary condition for a matroid to be linearly representable and it comes in the form of a linear inequality in its rank function. In a probability-theoretic reinterpretation of the inequality, linear subspaces are replaced by discrete random variables and ranks by Shannon entropies. In this setting, the Ingleton inequality no longer holds universally for representable rank functions but only if additional linear constraints are assumed.
In this talk, I give an overview of these so-called conditional Ingleton inequalities, their historical roots and my own contribution to finishing their classification for four discrete random variables.

Algebra and discrete mathematics seminar

Heini Kanerva

**Master thesis talk : Detection of spruces damaged by the European spruce bark beetle from unmanned aerial vehicle imagery using deep learning**

Friday 23 September 2022, 13:00, M134

Detection of spruces damaged by
the European spruce bark beetle
from unmanned aerial vehicle
imagery using deep learning

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Friday 23 September 2022, 09:30, Riihi (Y225a)

Further information

**Matematiikan kandidaattiseminaari / Bachelor seminar in mathematics**

Friday 23 September 2022, 09:15, Y308

Further information

Joe Thomas (Durham)

**Quantum Unique Ergodicity for random bases on Cayley Graphs**

Monday 19 September 2022, 14:15, M3 (M234)

The quantum unique ergodicity conjecture is a long-standing open problem concerning the extent to which eigenfunctions of the Laplacian on a manifold are delocalised in the presence of ergodic classical dynamics. Similar enquires have also taken place in the discrete setting which can be seen as a toy model for the continuous case. In this talk, I will review notions of quantum (unique) ergodicity in the setting of regular graphs. I will then discuss some recent joint work with Michael Magee (Durham) and Yufei Zhao (MIT) where we show the existence of an abundance of bases of eigenfunctions that satisfy a quantum unique ergodicity result in the setting of Cayley graphs.

Seminar / Tuomas Sahlsten

Elif Sacikara

**q-Analogues of Matroids**

Wednesday 14 September 2022, 16:15, M3 (M234)

In combinatorics, a q-analog of a discrete structure is defined by replacing finite sets with finite dimensional vector spaces. On the other hand, matroids are defined as a combinatorial abstraction of several objects such as linearly independent vectors or graphs.
In this talk, we first define a matroid with certain equivalent axiomatic definitions by supporting them with examples. Then we discuss their q-analogs by comparing differences and similarities with the classical case. Finally, as a construction and an application of a q-matroid, we mention their relation with a q-analog of other combinatorial objects called designs, and state some open questions.
This work is a part of the research project supported by Women in Numbers - Europe.

ANTA Seminar

Pavlo Yatsyna

**How many variables will it take?**

Wednesday 07 September 2022, 16:15, M3 (M234)

This talk will be about the representation of integers by quadratic forms. We will survey what is known about the quadratic forms that represent all eligible integers of totally real number fields. It will include the recent results, from the joint work with Vitezslav Kala, Dayoon Park, and Blazej Zmija, on the density of real quadratic number fields that have a universal quadratic form with a fixed number of variables.

ANTA Seminar

**Matematiikan kandidaattiseminaari / Bachelor seminar in mathematics**

Friday 02 September 2022, 09:15, M1 (M232)

Further information

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Friday 26 August 2022, 09:30, Riihi (Y225a)

Further information

Guilherme Sales Santa Cruz

**On Assessing Valuation Robots (Master's thesis presentation)**

Monday 15 August 2022, 15:15, Zoom

Further information

Dr Vinay Kumar BR (INRIA Sophia Antipolis)

**A probabilistic broadcast mechanism on random geometric graphs**

Friday 12 August 2022, 11:00, M3 (M234)

We consider the problem of energy-efficient broadcasting on homogeneous random geometric graphs (RGGs) within a large finite box around the origin. A source node at the origin encodes $k$ data packets of information into $n\ (>k)$ coded packets and transmits them to all its one-hop neighbors. The encoding is such that, any node that receives at least $k$ out of the $n$ coded packets can retrieve the original $k$ data packets. Every other node in the network follows a probabilistic forwarding protocol; upon reception of a previously unreceived packet, the node forwards it with probability $p$ and does nothing with probability $1-p$. We are interested in the minimum forwarding probability which ensures that a large fraction of nodes can decode the information from the source. We deem this a \emph{near-broadcast}. The performance metric of interest is the expected total number of transmissions at this minimum forwarding probability, where the expectation is over both the forwarding protocol as well as the realization of the RGG. In comparison to probabilistic forwarding with no coding, our treatment of the problem indicates that, with a judicious choice of $n$, it is possible to reduce the expected total number of transmissions while ensuring a near-broadcast. Techniques from continuum percolation and ergodic theory are used to characterize the probabilistic broadcast algorithm.
Joint work with Navin Kashyap and D. Yogeshwaran

Aalto Stochastic & Statistics Seminar / Lasse Leskelä

Dr. Matteo Mucciconi (University of Warwick)

**Some recent results in Integrable Probability**

Tuesday 02 August 2022, 14:00, M3 (M234)

In the last 25 years the study of solvable growth models related to the Kardar-Parisi-Zhang (KPZ) stochastic partial differential equation uncovered connections with a number of seemingly unrelated fields including representation theory, combinatorics, Integrable Systems and so on. This program, commonly referred to as Integrable Probability, delivered a host of remarkable successes, including the characterization of new universal processes or the explicit solution of the KPZ equation under certain initial data. In this talk I will review some of these progresses, highlighting some recent ones.

Mathematical physics seminar / Shinji Koshida

Vili Nieminen

**Local Poisson's Equation Approximation by Probabilistic Algorithm (Master Thesis talk)**

Thursday 21 July 2022, 14:00, M203

Konsta Holopainen

**On predicting performance in heart failure patients (Master's thesis presentation)**

Monday 27 June 2022, 14:15, M3 (M234)

Tuomo Valtonen (BSc presentation)

**List-decoding of Reed-Solomon codes**

Friday 17 June 2022, 11:00, M1 (M232)

ANTA Seminar

Olli Pasanen (Patria)

**On Bayesian methods for program authorship attribution**

Friday 17 June 2022, 10:15, M3 (M234)

**Matematiikan kandiseminaari / Bachelor seminar (mathematics)**

Friday 17 June 2022, 09:15, M1 (M232)

Further information

**Systeemitieteiden kandidaattiseminaari / Bachelor seminar in systems analysis**

Wednesday 15 June 2022, 09:30, Riihi (Y225a)

Further information

The link to the zoom-meeting is available from Juho Roponen

**Matematiikan kandiseminaari / Bachelor seminar (mathematics)**

Friday 10 June 2022, 09:15, M240

Further information

Kandityöesitelmät:
(n. 9.15) Henri Lahdelma: Lämpöyhtälön ratkaisujen sileys ja derivaattojen estimaatit.
(n. 9.45) Kasper Lahtonen: Investing with hidden Markov models.
(n. 10.15) Leo Laitinen: Homeogeenisen kappaleen MRI-signaali yleisteyillä gradienttikentillä.
Aihe-esittelyt (kandityöesitelmien jälkeen):
Joona Lindell,
Teemu Korhonen,
Tommi Huhtinen.

Joanna Bisch (University of Lille)

**Functions of symmetric Toeplitz matrices**

Tuesday 07 June 2022, 14:15, M3 (M234)

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