Department of Mathematics and Systems Analysis

Current

Lectures, seminars and dissertations

* Dates within the next 7 days are marked by a star.

Acadamy Research Fellow Kaisa Matomäki (University of Turku)
Correlations of arithmetic functions
* Tuesday 27 February 2018,   15:15,   D
Important arithmetic functions include the von Mangoldt function $\Lambda(n)$ which is essentially a weighted characteristic function of the primes, and the Liouville function $\lambda(n)$ which is $-1$ or $+1$ depending on whether $n$ has an odd or even number of prime factors. Mean values of these functions have been known for more than a century and in both cases the asymptotic evaluation of the mean value is equivalent to the prime number theorem which says that the number of primes up to $x$ is $x/\log x$. Much more difficult question is whether there is correlation between consecutive values of $\lambda(n)$ or between $\Lambda(n)$ and $\Lambda(n+2)$. Such questions are closely related to the notoriously difficult twin prime conjecture which claims that there are infinitely many primes $p$ such that $p+2$ is also prime. Though the twin prime conjecture is still a distant goal, there has been some recent progress on this sort of correlations which I will discuss.
Colloquim

Pekka Alestalo (Aalto University)
Extension of bilipschitz maps: A survey
* Wednesday 28 February 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Sebastian Schwarzacher (University of Bonn)
TBA
Wednesday 07 March 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Ilmari Kangasniemi (University of Helsinki)
TBA
Wednesday 14 March 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Teaching meeting
Tuesday 20 March 2018,   14:15,   Coffee room

Sylvester Eriksson-Bique (UCLA)
TBA
Wednesday 21 March 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

TBA
TBA
Friday 23 March 2018,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Antti Vähäkangas (Jyväskylä)
TBA
Friday 23 March 2018,   15:15,   M3 (M234)
Harmonic analysis and PDE seminar

Prof. Heikki Haario (Lappeenranta University of Technology)
TBA
Tuesday 27 March 2018,   15:15,   D
Colloquim

Augusto Gerolin (University of Jyväskylä)
Optimal Transport meets Density Functional Theory
Wednesday 28 March 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Amal Attouchi (University of Jyväskylä)
Qualitative properties of viscosity solutions of a degenerate or singular parabolic equation in non-divergence form.
Wednesday 11 April 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Prof. Peter Lindqvist (Norwegian University of Science and Technology)
TBA
Tuesday 24 April 2018,   15:15,   D
Colloquim

Departmental meeting
Tuesday 29 May 2018,   14:15,   Coffee room

Past events

Nick Lindemulder (TU Delft)
A randomized difference norm for vector-valued Bessel potential spaces
Friday 23 February 2018,   15:15,   Kumpula Exactum C124
In this talk we discuss a randomized difference norm characterization for Bessel potential spaces in the UMD Banach space-valued setting. The main ingredients are R-boundedness results for Fourier multiplier operators, which are of independent interest. As an application we characterize the pointwise multiplier property of the indicator function of the half-space on these spaces. All results are proved in the setting of weighted spaces
Harmonic analysis and PDE seminar

Pekka Lehtelä (Aalto)
Obstacle problem for the porous medium equation
Friday 23 February 2018,   14:15,   Kumpula Exactum C124
Harmonic analysis and PDE seminar

Jung-Tae Park (Seoul National University)
Global gradient estimates for measure data problems in nonsmooth domains
Wednesday 21 February 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Stavros Evdoridis, Antti Rasila
Conformal geometry study group (first meeting)
Tuesday 20 February 2018,   12:15,   Y225a (Riihi)
Further information
The goal of the meeting is to study the book Moduli of Families of Curves for Conformal and Quasiconformal Mappings, by Alexander Vasil'ev. Everybody interested in geometric complex analysis is welcome.
Conformal geometry study group

Marzieh Arabi Kakavand
Cyclic Subspace Codes
Wednesday 14 February 2018,   15:15,   M205
Subspaces codes are of great interest due to their applications to multiple sender-receiver schemes. As in classical algebraic coding theory, one of the most important research area in random network coding is the existence and construction of subspace codes and cyclic subspace codes with good parameters. Recently Etzion et al. have presented a method for constructing cyclic subspace codes, which includes some special kind of linearized polynomials, namely subspaces polynomials and also Frobenius mappings. This new approach, especially the representation of some families of subspace codes via polynomials, is a very interesting contribution to this area of research. Some of the research on cyclic subspace codes, it becomes relevant the following conjecture. Conjecture: For every positive integers n, k such that k < n/2, there exists a subspace cyclic code of size (q^n-1)/(q-1) in G_q(n,k) and minimum distance 2k-2. For a fixed natural number k<= n let G_q(n,k) denote the set of all subspaces of F_q^n of dimension k and we call it the k-Grassmannian. I will talk about the efforts that were done for solving this Conjecture.
ANTA seminar

Tuomas Orponen (University of Helsinki)
On uniformly rectifiable surfaces in the Heisenberg group
Wednesday 14 February 2018,   12:15,   M3 (M234)
Abstract: A closed set in a metric space X satisfies Condition B, if for all x in S and r > 0, there exist two balls, which are contained in B(x,r), have radii comparable to r, and are contained in two distinct components of X \ S. In R^n, an (n - 1)-regular set satisfying Condition B is known to contain big pieces of Lipschitz graphs, by a result of G. David. I discuss joint work with K. Fässler and S. Rigot, where we prove an analogue of the result for 3-regular sets in the first Heisenberg group.
Seminar on analysis and geometry

Stanislav Nagy (Charles University)
Unified approach to the theory of functional data depth
Wednesday 07 February 2018,   17:00,   M3 (M234)
Depth has become a quite popular concept in functional data analysis. In the talk we discuss its general framework. We show that most known functional depths can be classified into few groups, within which they share similar theoretical properties. We focus on uniform consistency results for the sample versions of these functionals, and demonstrate that some well-known approaches to depth assessment are hardly theoretically adequate.
Workshop on statistical depths and functional data analysis

Joni Virta (Aalto SCI)
Independent component analysis of multivariate functional data
Wednesday 07 February 2018,   16:15,   M3 (M234)
We extend a classic method of independent component analysis, the fourth order blind identification (FOBI), to vector-valued functional data. The use of multivariate instead of univariate functions allows for natural definitions for both the marginals of a random function and their mutual independence. Our model assumes that the observed functions are mixtures of latent independent functions residing in suitable Hilbert spaces, mixed with a bounded linear operator from the product space to itself. To enable the inversion of the covariance operator we make the assumption that the dependency between the mixed component functions lies in a finite-dimensional subspace. In this subspace we define fourth cross-cumulant operators and use them to construct a novel Fisher consistent method for solving the independent component problem for vector-valued functions. Finally, both simulations and an application to hand gesture data set are used to demonstrate the advantages of the proposed method over its closest competitors.
Workshop on statistical depths and functional data analysis

Sami Helander (Aalto SCI)
On typicality of functional observations
Wednesday 07 February 2018,   15:00,   M3 (M234)
Most of the functional depth approaches presented in the literature are solely interested in the -pointwise- centrality of the observations as a measure of (global) centrality. As a result, they are missing some important features inherent to functional data such as variation in shape, roughness or range. Thus, due to the richness of functional data, we opt to talk about typicality rather than centrality of an observation. We discuss assessing typicality of functional observations. Moreover, we provide a new concept of depth for functional data. It is based on a new multivariate Pareto depth applied after mapping the functional observations to a vector of statistics of interest. These quantities allow incorporating the inherent features of the distribution, such as shape or roughness. In particular, in contrast to most existing functional depths, the method is not limited to centrality only. Properties of the new depth are explored and the benefits of a flexible choice of features are illustrated.
Workshop on statistical depths and functional data analysis

Germain Van Bever (Université libre de Bruxelles)
Halfspace depths for scatter, concentration and shape matrices
Wednesday 07 February 2018,   14:15,   M3 (M234)
We propose halfspace depth concepts for scatter, concentration and shape matrices. For scatter matrices, our concept extends the one from Chen, Gao and Ren (2015) to the non-centered case, and is in the same spirit as the one in Zhang (2002). Rather than focusing, as in these earlier works, on deepest scatter matrices, we thoroughly investigate the properties of the proposed depth and of the corresponding depth regions. We do so under minimal assumptions and, in particular, we do not restrict to elliptical distributions nor to absolutely continuous distributions. Interestingly, fully understanding scatter halfspace depth requires considering different geometries/topologies on the space of scatter matrices. We also discuss, in the spirit of Zuo and Serfling (2000), the structural properties a scatter depth should satisfy, and investigate whether or not these are met by the proposed depth. As mentioned above, companion concepts of depth for concentration matrices and shape matrices are also proposed and studied.
Workshop on statistical depths and functional data analysis

Ratan Kumar Giri (National Institute of Technology Rourkela, India)
Reduced limit corresponding to the second order semilinear elliptic PDEs with measure data
Wednesday 07 February 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Teaching meeting
Tuesday 06 February 2018,   14:15,   Coffee room

Pekka Pankka (University of Helsinki )
Deformation of cubical Alexander maps
Wednesday 31 January 2018,   12:15,   M3 (M234)
I will discuss parts of a recent work with Jang-Mei Wu related to extension theory of spatial quasiregular mappings. The talk is mostly on the topological/combinatorial aspects of the extension theory and I will focus on a certain class PL branched covers, called cubical Alexander maps, and their branched cover homotopy theory following Rickman's ideas. As a particular result I will discuss a version of the Hopf theorem in this category: Two cubical and cubically shellable Alexander maps of an n-sphere are branched cover homotopic if and if they have the same degree.
Seminar on Analysis and Geometry

Prof. Petteri Kaski (Aalto Univeristy)
Proofs and computation
Tuesday 30 January 2018,   15:15,   D
A highly desirable property for a mathematical proof is that its correctness is easier to verify than it is to prepare the proof from scratch. One possibility to quantify such "ease of verification" is to view the tasks of preparing and verifying a proof from a computational perspective and in terms of the computational resources employed for a task. Indeed, such proof-system-based characterizations are in many ways fundamental to our current understanding of computational complexity and complexity classes such as P, NP, and beyond. This talk explores classical and recent work on proof systems for computational problems, including some of our own recent work involving proof systems that tolerate adversarial errors during proof preparation.
Colloquim

Teemu Murtola (University of Tampere, Faculty of Medicine and Life Sciences)
Benefits of cholesterol-lowering statins in prostate cancer
Tuesday 30 January 2018,   10:00,   M3 (M234)
Many commonly used drugs target intracellular signaling pathways that have importance in carcinogenesis and progression of cancer. One example is the mevalonate pathway which is targeted by cholesterol-lowering statin drugs. Examining possible anticancer effects of drug groups established for other indications requires comprehensive multidisciplinary approach including epidemiological studies to explore associations with cancer risk and prognosis, experimental laboratory studies to elucidate possible anticancer mechanisms and ultimately clinical trials to test for clinical benefit. This lecture describes such project testing statins' effects against prostate cancer.
Aalto Stochastics and Statistics Seminar

Jari Miettinen (Aalto ELEC)
Independent component analysis for graph data using graph-autocorrelation matrices
Monday 29 January 2018,   15:15,   M3 (M234)
The first independent component analysis estimators were designed for i.i.d. data, and they assume that at most one of the independent components has Gaussian density. Afterwards, methods have been developed for data with dependencies between the observations, including for example time series and spatial data. Those methods utilize solely or partially the structure of the data. For the most general case, graph data, Blochl et al. introduced an ICA estimator called GraDe (graph decorrelation) which uses approximate joint diagonalization of graph-autocorrelation matrices. GraDe contains the best-known time series and spatial methods as special cases. The structure of the graph is given in an adjacency matrix which is to be known or estimated prior to performing the ICA task. As one example in our paper on the effects of adjacency matrix estimation errors in graph signal processing, we study how the GraDe method is affected by misspecification of the adjacency matrix, using both theoretical and simulation results.
Aalto Stochastics and Statistics Seminar

Stefan Sturm (Universität Salzburg)
Regularity of weak solutions and supersolutions to the porous medium equation
Friday 26 January 2018,   15:15,   M3 (M234)
Harmonic analysis and PDE seminar

Paolo Marcellini (Università di Firenze)
Elliptic and parabolic equations under general and p,q growth conditions
Friday 26 January 2018,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Jouni Parkkonen (University of Jyväskylä)
Equidistribution and counting in negatively curved spaces
Wednesday 24 January 2018,   12:15,   M3 (M234)
Seminar on analysis and geometry

Mindaugas Bloznelis (U Vilnius)
Local probabilities of randomly stopped sums of power law lattice random variables and clustering patterns in complex networks
Monday 22 January 2018,   15:15,   M3 (M234)
Let $X_1$ and $N$ be non-negative integer valued power law random variables. For a randomly stopped sum $S_N=X_1+\cdots+X_N$ of independent and identically distributed copies of $X_1$ we establish a first order asymptotics of the local probabilities $P(S_N=t)$ as $t\to+\infty$. Using this result we show the $k^{-\delta}$, $0\le \delta\le 1$ scaling of the local clustering coefficient (of a randomly selected vertex of degree $k$) in a power law affiliation network. http://arxiv.org/abs/1801.01035
Aalto Stochastics & Statistics Seminar

Prof. Ralph L. Keeney
Value-Focused Decisions
Thursday 18 January 2018,   16:00,   hall E
Further information
Aalto Systems Forum

Laia Amoros Carafi
Arithmetic of quaternion algebras and Shimura curves
Wednesday 17 January 2018,   15:15,   M205
I will introduce quaternion algebras and show how one can construct Shimura curves with them. Quaternion algebras arise as a natural generalisation of matrix algebras. In the same way that the action of SL(2,Q) (and of all its congruence subgroups) on the complex upper half-plane give us modular curves, the action of certain subgroups of quaternion algebras will give us some algebraic structure (the so called Shimura curves). After this introduction I will explain some applications of Shimura curves and sketch how one can compute the bad reduction of certain families Shimura curves, based on a joint work with P. Milione.
ANTA seminar

Timmavajjula Venkata Karthik (IISER)
Symmetric group action on the cohomology algebra of configuration space of particles in R^3
Wednesday 20 December 2017,   14:15,   M3 (M234)
We first give a brief introduction to the physics of the problem followed by descriptions of the cohomology algebra(H_n^∗) and the action of the symmetric group Σ_n on it, accompanied by computations for a few values of n. Then we get to our main aim which is: Determining the multiplicity(μ_{k,d,n}) of the k:th hook representation of S_n in H_n^d, by describing the Hook representations, Lehrer’s generating function method for computing characters of both representations of symmetric group on the algebra as well as that of Hook representations. Finally, using combinatorial techniques such as Moreau's Necklace counting function and the cyclotomic identity, we determine μ_{0,d,n}, μ_{n−1,d,n} and finally the general case μ_{k,d,n}.
Kytölä / Radnell

Eveliina Peltola (University of Geneva)
Multiple SLEs for \kappa \leq 4
Tuesday 19 December 2017,   15:45,   U3
Further information
Stochastic Sauna 2017 / Kytölä, Leskelä, Radnell, Webb

Mikko Pakkanen (Imperial College London)
Rough volatility: towards efficient Monte Carlo pricing and calibration
Tuesday 19 December 2017,   14:30,   U3
Further information
Stochastic Sauna 2017 / Kytölä, Leskelä, Radnell, Webb

Roland Bauerschmidt (University of Cambridge)
Eigenvectors and spectral measure of random regular graphs of fixed degree
Tuesday 19 December 2017,   13:30,   U3
Further information
Stochastic Sauna 2017 / Kytölä, Leskelä, Radnell, Webb

Dr David Cushing (Durham University)
Ollivier-Ricci idleness functions of graphs
Tuesday 19 December 2017,   12:15,   M2 (M233)
Ricci curvature plays a very important role in the study of Riemannian manifolds. In the discrete setting of graphs, there is very active recent research on various types of Ricci curvature notions and their applications. One such notion on graphs is the Ollivier-Ricci curvature. This notion has recently had many applications, ranging from modelling cancer growth to modelling WiFi connections. This stems from this curvature notion being a way to quantify local connectedness. Ollivier-Ricci curvature is motivated by optimal transport. I will begin by giving a crash course on optimal transport theory and defining Ollivier-Ricci curvature on graphs. Then we will study the Ollivier-Ricci curvature of graphs as a function of the chosen idleness. We show that this idleness function is concave and piecewise linear with at most 3 linear parts, with at most 2 linear parts in the case of a regular graph. We then apply our result to show that the idleness function of the Cartesian product of two regular graphs is completely determined by the idleness functions of the factors.
Discrete geometry seminar / Kangaslampi

Lauri Viitasaari (University of Helsinki)
On model fitting and estimation of stationary processes
Tuesday 19 December 2017,   11:15,   U3
Further information
Stochastic Sauna 2017 / Kytölä, Leskelä, Radnell, Webb

Aristides Gionis (Aalto University)
Mining temporal networks
Tuesday 19 December 2017,   10:15,   U3
Further information
Stochastic Sauna 2017 / Kytölä, Leskelä, Radnell, Webb

Oscar Kivinen (UC Davis)
Hilbert schemes of singular plane curves and knot homology
Tuesday 12 December 2017,   14:15,   M3 (M234)
Conjectures of Gorsky, Oblomkov, Rasmussen, Shende and others relate the homologies of Hilbert schemes of points on plane curve singularities to homological invariants of the corresponding links. Representation-theoretic approaches to these conjectures have borne fruit in the case of torus links. I will give an overview of these conjectures and discuss how a subalgebra of the Weyl algebra acting on the homologies of the Hilbert schemes in question gives us a way to approach them, focusing on computations and simple examples.
Engström / Kytölä

Prof. Felix Schwenninger (University of Hamburg)
Around the inverse generator problem
Tuesday 12 December 2017,   14:15,   M2 (M233)

Alex Karrila
Uniform spanning trees, scaling limits, and conformal invariance
Tuesday 12 December 2017,   12:05,   M205
Doctoral student talk / Engström

Joona Karjalainen
Moment-based parameter estimation in random intersection graphs
Tuesday 12 December 2017,   11:40,   M205
Doctoral student talk / Engström

Matias Heikkilä
On multivariate separating Hill estimator under estimated location and scatter
Tuesday 12 December 2017,   11:15,   M205
Doctoral student talk / Engström

Casimir Lindfors
On the degenerate two-phase Stefan problem
Friday 01 December 2017,   15:15,   M3 (M234)
Harmonic analysis and PDE seminar

Ella Tamir (Helsinki)
Constructing the Green function for a non-coercive PDE
Friday 01 December 2017,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Prof. Kari Astala (Aalto University)
Random tilings, variational problems and the Beltrami equation.
Tuesday 28 November 2017,   15:15,   U1
Interactions between analysis and random geometry is a topical area in mathematics. In two dimensions, in particular, limit configurations of random structures often posses some conformal invariance properties, giving way to methods of geometric analysis. In this talk, based on joint work with E. Duse, I. Prause and X. Zhong, I describe our project where our goal is to apply methods of geometric analysis in describing limit configurations of random tilings, and parametrizations of the boundaries between the ordered and disordered, or liquid, limit regions. It turns out that the liquid domains carry a natural complex structure described by a quasilinear Beltrami equation, with surprising properties.
Colloquim

Taneli Luotoniemi (Aalto University)
Hyperspatial Intuitions Through Visual Props
Wednesday 22 November 2017,   12:15,   M3 (M234)
Four-dimensional space is a mathematical thought experiment of adding an extra spatial dimension perpendicular to our three dimensions of length, height and width. Originating in philosophy and mathematically formulated in geometry, the concept has evoked interpretations not only in theoretical physics and visual arts, but also in occultism and science fiction. Research on its properties is made possible by generalizing the methods acquired by studying more familiar spaces of lower dimensions. Just as 3-dimensional structures can be drawn, unfolded, sliced, photographed, or otherwise flattened onto a planar medium like paper or computer screen, these techniques can be generalized to produce 3D manifestations of various 4-dimensional structures. These objects provide a sensuous access to a provokingly counter-intuitive, but nevertheless logically consistent concept rich with scientific, historical and poetic significance.
Seminar on analysis and geometry

Joonas Pääkkönen
On an equality in wirless communications
Wednesday 15 November 2017,   15:15,   M205
In modern wireless communication systems, it is a well-known assumption that the received signal amplitude is $y = hx + n$, where $x$ is the transmitted amplitude, $h$ is the fading coefficient and $n$ is thermal receiver noise. This model has been the bedrock for deriving a myriad of mathematical results. However, it might be forgotten that this model does not always apply. In this lecture-like, rather informal talk, I will not present new results, but show from where this formula comes and under what circumstances it is reasonable.
ANTA seminar

Lauri Hitruhin (University of Helsinki)
Stretching and rotational multifractal spectra of mappings with integrable distortion
Wednesday 15 November 2017,   12:15,   M3 (M234)
Seminar on analysis and geometry

Vilma Virasjoki
Models for the Sustainable Transition of Energy Markets
Tuesday 14 November 2017,   12:15,   M205
Doctoral student talk / Engström

Edoardo Tosoni
Safety assessment of nuclear waste repositories
Tuesday 14 November 2017,   11:40,   M205
Doctoral student talk / Engström

Alessandro Mancuso
Portfolio optimization of risk management actions in safety critical systems
Tuesday 14 November 2017,   11:15,   M205
Doctoral student talk / Engström

Emil Vuorinen (Helsinki)
A representation theorem for bilinear singular integrals
Friday 10 November 2017,   15:15,   Kumpula Exactum C124
Harmonic analysis and PDE seminar

Matias Vestberg (Aalto)
An Excursion in Shallow Water
Friday 10 November 2017,   14:15,   Kumpula Exactum C124
We take a stroll in the world of shallow water dynamics as described by the diffusive wave approximation. This nonlinear parabolic PDE is used to model floods and dam breaks, and can be seen as a generalization of both the parabolic p-Laplace equation and the porous medium equation. We review results concerning local boundedness for weak solutions, and discuss in detail the fundamental solutions and their properties.
Harmonic analysis and PDE seminar

Marzieh Arabi Kakavand
On the Locality of Codeword Symbols
Wednesday 08 November 2017,   15:15,   M205
Consider a linear $[n, k, d]_q$ code $C$. The $i$th coordinate of $C$ has locality $r$, if the value at this coordinate can be recovered from accessing some $r$ other coordinates of $C$. Data storage applications require codes with low locality for information coordinates and low locality for parity coordinates. Motivated by applications to data storage, Gopalan and his collaborators (2012) introduce $(r, d)$-codes, which are systematic codes that have distance $d$ and also have the property that any information coordinate has locality $r$ or less. In this presentation, I will talk about results that are obtained on the linear codes and nonlinear codes with locality property.
ANTA seminar

Laura Venieri (University of Helsinki)
A Marstrand-type theorem for a one-dimensional family of projections in R^3
Wednesday 08 November 2017,   12:15,   M3 (M234)
Marstrand's projection theorem in R^3 states that the Hausdorff dimension of the projection of a set onto almost every line is the minimum between one and the dimension of the set. Here almost every is intended with respect to the surface measure on the sphere. In this talk I will show an improvement of the theorem based on joint work with A. Käenmäki and T. Orponen: the same conclusion holds if we replace the surface measure with the length measure on certain curves on the sphere.
Seminar on analysis and geometry

David Radnell (Aalto University)
Model of the Teichmuller space of genus-zero bordered surfaces by period maps
Wednesday 01 November 2017,   12:15,   M3 (M234)
The classical period mapping takes compact Riemann surfaces of genus g into the Siegel upper half-plane, which consists of symmetric g x g matrices with positive definite imaginary part. It is a classical fact that this map is holomorphic. We generalize the period mapping to the case of the Teichmuller space of genus-zero surfaces with n closed non-overlapping disks removed and prove it is holomorphic. The period mapping takes the Teichmuller space of this type into the direct product of the Teichmuller space of genus-zero surfaces with n punctures and a space of bounded operators on an n-fold sum of Bergman spaces of the disk. The construction relies on a generalization of the classical Grunsky operator, new extension and reflection results on quasidisks, as well as a coordinate system for the infinite-dimensional Teichmuller space inspired by conformal field theory. This talk will introduce these results which are joint work with Eric Schippers and Wolfgang Staubach. Background notions will be explained and technical details will be hidden.
Seminar on analysis and geometry

Prof. Lothar Nannen (TU Wien)
Numerical methods for resonance problems in open systems
Tuesday 31 October 2017,   15:00,   U1
Colloquim

Dissertation
Lauri Mustonen, Prof. Roland Griesmaier (Wuerzburg)
Approximations and surrogates for computational inverse boundary value problems
Friday 27 October 2017,   12:00,   M1 (M232)

Prof. Roland Griesmaier (University of Wuerzburg)
Uncertainty principles for far field patterns and applications to inverse source problems
Thursday 26 October 2017,   12:30,   M2 (M233)
Seminar on Applied Mathematics

Emil Sköldberg
The homologies of monomial ideals and incidence algebras.
Wednesday 25 October 2017,   15:15,   M2 (M233)
Given a set of monomials M ={m_1, ..., m_r} in a polynomial ring, one can form the set L of all least common multiples of subsets of M. This set is a partially ordered set, (even a lattice) ordered by divisibility. It is known that the betti numbers of the ring S/(M) can be computed as the homology of the simplicial complex of L. In the talk, I will explain how this relationship can be lifted to hold on the level of resolutions, between modules over S on one hand, and modules over the incidence algebra of L on the other hand.
ANTA seminar

Jia Huilian (Aalto Xián Jiaotong University)
Global regularity of elliptic p-Laplace equation on convex domain
Friday 20 October 2017,   15:15,   M3 (M234)
Harmonic analysis and PDE seminar

Tuomas Hytönen (Helsinki)
The matrix-weighted frontier of sharp norm inequalities
Friday 20 October 2017,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Stavros Evdoridis
Bohr's inequality for harmonic mappings
Wednesday 18 October 2017,   12:15,   M3 (M234)
Seminar on analysis and geometry

Robin Rajamäki
Additive 2D bases
Wednesday 11 October 2017,   15:15,   M2 (M233)
Additive bases, i.e. sets of integers whose pairwise sums cover a desired set of integers, have been studied by number theorists since the early 20th century. In particular, the combinatorial problem of minimizing the number of elements required to cover a given set of consecutive integers is often of interest. Such optimal bases find applications in e.g. sparse linear sensor arrays, where the number of sensors is desired to be kept low in order to reduce costs and mitigate non-ideal coupling effects between array elements. Although much of the existing work on additive bases is directly applicable to 1D sparse array design, often 2D arrays are required in practice. However, additive 2D bases have not been studied as extensively as their 1D counterpart in the past. In our talk, we present some recent results on rectangular additive bases, i.e. additive bases whose sumsets cover a rectangular area of consecutive points in the plane. For example, optimal rectangular bases found through exhaustive computer search are shown. Furthermore, different rectangular bases with analytically tractable structure and a low element count are introduced.
ANTA seminar

Galia Dafni (Concordia University)
Local BMO and Van Schaftingen spaces
Wednesday 11 October 2017,   12:05,   M3 (M234)
Abstract: Based on an inequality of Bourgain and Brezis, Van Schaftingen introduced a scale of function spaces lying between the critical Sobolev space and BMO, and suggested that an analogous result should hold in the case of local BMO spaces on domains. We discuss recent work of A. Butaev, who constructed nonhomogeneous versions of Van Schaftingen spaces on Euclidean space, as well as on manifolds, and showed that they lie between the critical Sobolev space and the space bmo, defined by Goldberg. Moreover, he proved a corresponding version for the nonhomogeneous space of functions of vanishing mean oscillation (vmo). On a Lipschitz domain $\Omega$, Butaev answered the question of Van Schaftingen by showing that there are two scales of spaces lying between $W^{1,n}(\Omega)$ and $W^{1,n}_0(\Omega)$, respectively, and the local BMO spaces bmo_r and bmo_z studied by Chang-Krantz-Stein and Chang-Dafni-Stein.
Seminar on analysis and geometry

Kristian Moring (Diploma thesis talk)
Direct methods in the calculus of variations for parabolic problems
Thursday 05 October 2017,   15:15,   M3 (M234)

Niko Väisänen (Nokia/Aalto)
Beamforming -- Enabling Higher Data Rate Wireless Communications
Thursday 05 October 2017,   15:15,   M205
MSc thesis presentation
ANTA

Mateus Sousa (IMPA, Rio de Janeiro)
Existence for Fourier restriction on hyperboloids
Thursday 05 October 2017,   14:15,   M3 (M234)
In this talk we present some results about existence, as well as non existence, of extremizers for the adjoint Fourier restriction estimate on hyperboloids. We will discuss the Lorentz symmetries of the problem and the concentration-compactness arguments involved in the proofs, as well as connections to the Klein-Gordon equation.

Negin Karimi
LCD codes
Wednesday 04 October 2017,   15:15,   M3 (M234)
Error-correcting codes play an important role in digital communication among all types of codes. Linear codes are studied the most. Because of their algebraic structure, they are easier to describe, encode, and decode than nonlinear codes. A special class of linear codes is linear complementary dual code (LCD code). LCD codes are defined by Massy in 1992. He was shown that asymptotically good codes exist. LCD codes have been widely applied in data storage, communications systems, and cryptography. Also, they are interesting objects in the general framework of algebraic coding. In this talk will be presented some of the properties cyclic codes, quasi-cyclic codes and quasi-twisted codes with complementary dual.
ANTA seminar

Juha Videman (University of Lisbon)
A degenerate elliptic-parabolic system arising in competitive contaminant transport
Wednesday 04 October 2017,   12:15,   M3 (M234)
The transport of contaminants in subsurface environments is a complex process modeled by advection-diffusion-reaction equations. If the reactive adsorption process (accumulation of a pollutant on the porous matrix) is described by a nonlinear isotherm of Freundlich type, the evolution of the solute concentrations is governed by a degenerate parabolic equation. In the multi-species case (contamination by several solutes), this corresponds to a coupled system of degenerate elliptic-parabolic equations. After introducing the basic concepts of modeling contaminant transport in porous media, I will show that this system admits a unique weak solution provided the nonlinear adsorption isotherm associated with the reaction process satisfies certain physically reasonable structural conditions. Under these conditions, the system falls under the general quasi-linear elliptic-parabolic systems addressed by Alt and Luckhaus in their seminal work [1]. The main difference between our approach and that of [1] lies in the existence proof which we base on Rothes method and on solving a convex minimization problem at each time step. Our approach provides also a simple method for the numerical approximation of the system. This is a joint work with Margarida Baia (CAMGSD/IST), Farid Bozorgnia (CAMGSD) and Leonard Monsaingeon (CAMGSD/Universite de Lorraine). [1] W. H. Alt and S. Luckhaus, Quasilinear Elliptic-Parabolic Di erential Equations, Math. Z. 183 (1983), 311-341.
Seminar on analysis and geometry

Timo Hänninen (HY)
Two-weight Lp-Lq bounds for positive dyadic operators in the case 0
Friday 29 September 2017,   15:15,   Kumpula Exactum C124
Harmonic analysis and PDE seminar

Thomas Singer (Aalto)
Existence of variational solutions in non-cylindrical domains
Friday 29 September 2017,   14:15,   Kumpula Exactum C124
Harmonic analysis and PDE seminar

Esko Heinonen (University of Helsinki)
Existence and non-existence results for minimal graphic and p-harmonic functions
Wednesday 27 September 2017,   12:15,   M3 (M234)
In the Euclidean space, by the celebrated result due to Bombieri, De Giorgi, and Miranda, all positive entire solutions of the minimal graph equation are constant. It turns out that on Riemannian manifolds similar results can be obtained for solutions with at most linear growth if the manifold has only one end and asymptotically non-negative sectional curvature. In this talk I will discuss about recent results concerning the existence and non-existence of entire minimal graphic and p-harmonic functions. Talk is based on joint work with Jean-Baptiste Casteras and Ilkka Holopainen.
Seminar on analysis and geometry

Prof. Daniele Boffi (Università di Pavia, Aalto University)
Finite element approximation of resonant modes for the Maxwell cavity problem
Tuesday 26 September 2017,   15:15,   M1 (M232)
The resonant modes of time harmonic Maxwell equations can be identified with the eigensolutions of a problem represented by a variational formulation in mixed form. In this talk we review the finite element approximation of eigenvalue problems arising from partial differential equations. In particular, it will be shown that the analysis of mixed problems differs significantly from that of standard Galerkin formulations. We will show how these results can be applied to the a priori analysis of Maxwell's eigenvalue problem and we will give some indications on how the a posteriori analysis can be performed
Colloquim

Lauri Harhanen (KaVo Kerr), Antti Huhtala (SSF), Saara Hyvönen (DAIN Studios), Mika Juntunen (KONE), Juho Könnö (Wärtsilä), Otto Seiskari (IndoorAtlas), Stratos Staboulis (Eniram)
Sovelletut matemaatikot teollisuudessa
Thursday 21 September 2017,   14:00,   U6, Otakaari 1

Jeff Lindquist (University of California, LA)
Weak capacity in Ahlfors regular metric spaces
Wednesday 20 September 2017,   12:15,   M3 (M234)
We construct and use a hyperbolic filling of a $Q$-regular compact doubling metric space $Z$ to define the notion of the weak $p$-capacity between appropriate subsets of $Z$. This notion extends modulus and is preserved up to constants by quasisymmetric maps. We explore some applications involving Ahlfors regular conformal dimension and quasisymmetric uniformization of metric 2-spheres.
Seminar on analysis and geometry

Tuomo Tiilikainen
Lämpöyhtälön keskiarvoperiaate/Diplomityöesitelmä
Wednesday 13 September 2017,   15:15,   M2 (M233)

Ilmari Kangasniemi (University of Helsinki)
Cohomological behavior of uniformly quasiregular mappings
Wednesday 13 September 2017,   12:15,   M3 (M234)
Based on a joint work with Pekka Pankka. Given a uniformly quasiregular map f on a closed oriented Riemannian manifold, it turns out that all the complex eigenvalues of the induced pull-back map f* in real singular cohomology have a modulus of (deg f)^(k/n), and moreover the induced cohomological map is complex diagonalizable. This can be exploited to obtain limitations on the possible degrees of uniformly quasiregular maps on closed manifolds. The talk goes over some basics and context regarding uniformly quasiregular mappings, and presents the main ideas behind the proofs of the aforementioned results.
Seminar on analysis and geometry

D.Sc (Tech) Antti Punkka
Teaching demonstration: Pareto-optimality in solving multicriteria optimization problems
Friday 08 September 2017,   10:30,   M2 (M233)

Jan Hämäläinen
Elementtimenetelmä magnetostatiikassa
Thursday 07 September 2017,   11:15,   M237
Kandiseminaari

Tarmo Kivioja
Lokaalin sileyden estimoinnista
Thursday 07 September 2017,   10:15,   M237
Kandiseminaari

Ville Kujala
Achieving the capacity of coded PIR using arbitrary linear code (BSc presentation)
Friday 25 August 2017,   15:15,   M3 (M234)
Kandidaattiseminaari

Juuso Korvuo
Hilojen lähimmän vektorin ongelma (kandiesitelmä)
Thursday 24 August 2017,   14:15,   M3 (M234)
Kandidaattiseminaari

Aki Malinen
Algebraic methods in maximum likelihood estimation (BSc presentation)
Thursday 24 August 2017,   09:15,   M3 (M234)
Kandidaattiseminaari

Hoa Ngo [Stochastic afternoon]
Information spreading in a large network
Tuesday 22 August 2017,   16:10,   M3 (M234)
A simple mathematical model for information spreading is a complete graph where everyone knows everyone and everyone relays messages at random time instants to randomly chosen neighbours independently of each other. In this talk we will consider information spreading in the large configuration model, which is a more advanced model. One of the key quantity analysing the rumour spreading speed is the broadcast time, the time when the rumour has reached the entire population. We will also discuss the broadcast time taking into account the passive and active users.

Alex Karrila [Stochastic afternoon]
Boundary branches in a uniform random spanning tree of a planar graph
Tuesday 22 August 2017,   15:10,   M3 (M234)
A physics principle asserts that the scaling limit of a critical lattice model, as increasingly dense lattices approximate a continuum domain, is described by a conformal field theory (CFT). The aim of this talk is to prove rigorously conformal invariance properties in the scaling limit of the uniform spanning tree (UST) of a planar graph, i.e., a tree subgraph that covers all the vertices of the original graph, chosen uniformly at random. In a spanning tree, any two vertices are connected by a unique path, called a branch. We study multiple simultaneous UST boundary-to-boundary branches between given boundary vertices, as well as the boundary visits of a single such branch. The related probabilities have conformally invariant scaling limits, and solve partial differential equations as predicted by CFT. As a collection of curves, such multiple simultaneous branches converge weakly to a conformally invariant law, called the local multiple SLE(2). These are among the first verifications of third-order PDEs of CFT, as well as convergence results to multiple SLE.

Armando W. Gutiérrez [Stochastic afternoon]
The horofunction compactificacion of lp spaces and Hilbert's projective metric
Tuesday 22 August 2017,   14:00,   M3 (M234)
The horofunction compactification is the result of making any metric space into a compact topological space by only using the metric. The elements of this compactification have been recently shown to be very useful in the study of limit theorems for deterministic and random dynamical systems. In this talk I will give a complete description of the horofunction compactification of the classical lp spaces. I will also consider Hilbert's projective metric on the standard cone of positive real vectors, and describe its horofunction compactification. The latter will be used to give a new proof of the well-known Perron theorem.

Valentina Candiani (University of Genova)
The role of segmentation in kidney compartmental analysis
Tuesday 22 August 2017,   10:15,   M2 (M233)
Seminar on Applied Mathematics

Prof. Saminathan Ponnusamy (ISI Chennai/IIT Madras)
Bohr radius
Wednesday 16 August 2017,   12:15,   M3 (M234)
Seminar on Analysis and Geometry

Mikko Kivelä (Aalto University)
Randomized reference models and spreading in temporal networks
Monday 14 August 2017,   15:15,   M3 (M234)
For a long time network science concentrated on static graphs as representations of networked systems. This abstraction was used to analyse shortest path lengths, spreading of disease or information in networks, and many other things. Often the underlying assumption behind such analysis was that the activation of nodes and links is controlled by homogeneous Poisson processes. More recently there has been growing interest in analysing 'temporal networks' where the link activation times are determined directly from data. In this talk I will illustrate how this approach can be used to analyse a large communication network with hundreds of millions of link activation events. I will focus on how 'reference models', in which the data is shuffled in various ways, can be used for this data and how they are used in the literature on temporal networks in general. I will also discuss the challenges in the literature that are caused by the sudden increase in use of such shuffling methods of temporal network.
Aalto Stochastics & Statistics Seminar

Kaisa Nyberg / Chris Brzuska
Connections between linear and statistical independence of binary random variables / Survey about indistinguishability obfuscation
Monday 14 August 2017,   14:30,   M2 (M233)
Informal presentations during the visit of our new Cryptology professor Chris Brzuska
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Dissertation
Vesa Kaarnioja, Prof. Lars Grasedyck (RWTH Aachen University)
On sparse tensor structures in lattice theory and applications of the polynomial collocation method based on sparse grids
Wednesday 02 August 2017,   12:00,   M1 (M232)
Further information

Leevi Korkeala
Hyperbolisten ryhmien pinta-aliryhmät (kandiesitelmä)
Wednesday 02 August 2017,   11:15,   M3 (M234)
Kandidaattiseminaari

Miio Taarna
Julkisen liikenteen verkostojen tarkastelu verkkoteorian keinoin (kandiesitelmä)
Wednesday 02 August 2017,   10:15,   M3 (M234)
Kandidaattiseminaari

Pauliina Kärkkäinen
Positroniemissiotomografian käänteisongelma
Wednesday 02 August 2017,   09:15,   M3 (M234)
Kandidaattiseminaari

Valtteri Lipiäinen
Verkkojen Ollivier-Ricci -kaarevuus (kandiesitelmä)
Thursday 20 July 2017,   11:15,   M3 (M234)
Kandidaattiseminaari

Miika Leinonen
Kvaternioalgebrat ja hyvin pyöristyvät hilat (kandiesitelmä)
Thursday 20 July 2017,   10:15,   M3 (M234)
Kandidaattiseminaari

Prof. Gonzalo R. Arce (University of Delaware)
Coded Aperture Optimization in Compressive X-ray Tomography
Thursday 06 July 2017,   13:15,   M205
Seminar on Applied Mathematics

Prof. Oktay Olmez, Ankara University
Binary three-weight linear codes from partial geometric difference sets
Wednesday 21 June 2017,   15:00,   M3 (M234)
Links between linear codes, non-linear functions from cryptography, graphs and combinatorial designs have attracted the attention of many researchers over the last 50 years. Difference set method is a powerful tool to construct designs and explore the links between designs and many other combinatorial objects including codes and nonlinear cryptographic functions. In this talk, we will introduce a generalisation of $(v,k,\lambda)-$difference sets known as partial geometric difference sets. In particular, we will show that existence of a family of partial geometric difference sets is equivalent to existence of a certain family of three-weight linear codes. We also provide a link between binary plateaued functions, three-weight linear codes and partial geometric difference sets.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Kurkela, Korkeala, Stenbacka, Wilkman, Hämäläinen ja Taarna
Kanditöiden aihe-esittelyt, sessio 3
Monday 19 June 2017,   15:00,   M3 (M234)
Sessiossa kandityönsä aiheen esittelevät Lauri Kurkela, Leevi Korkeala, Filip Stenbacka, Markus Wilkman, Jan Hämäläinen ja Miio Taarna
Hollanti & Kangaslampi

Kiuru, Kivioja, Kujala, Malinen, Hyytiäinen ja Koskinen
Kanditöiden aihe-esittelyt, sessio 2
Monday 19 June 2017,   14:00,   M3 (M234)
Sessiossa kandityönsä aiheen esittelevät Aukusti Kiuru, Tarmo Kivioja, Ville Kujala, Aki Malinen, Tatu Hyytiäinen ja Tuomas Koskinen
Hollanti & Kangaslampi

Kärkkäinen, Lipiäinen, Tuomala, Aaltonen, Korvuo ja Leinonen
Kanditöiden aihe-esittelyt, sessio 1
Monday 19 June 2017,   13:15,   M3 (M234)
Sessiossa kandityönsä aiheen esittelevät Pauliina Kärkkäinen, Valtteri Lipiäinen, Lari-Matti Tuomala, Tuuli Aaltonen, Juuso Korvuo ja Miika Leinonen
Hollanti & Kangaslampi

Christopher Hopper
Fractional differentiability and singular set bounds for holonomic minimisers of integral functionals
Friday 09 June 2017,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Dr. Fabricio Oliveira (RMIT Australia)
An introduction to Stochastic programming: modelling and solving decision problems under uncertainty
Wednesday 07 June 2017,   11:00,   M2 (M233)
Teaching demonstration

Dr. Fabricio Oliveira (RMIT Australia)
Efficiently solving stochastic mixed-integer problems combining Gauss-Seidel and penalty-based methods
Wednesday 07 June 2017,   09:00,   M2 (M233)

Cordian Riener (Kontanz + Arctic University)
Semidefinite programming and arithmetic progressions
Thursday 01 June 2017,   16:45,   M240
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Louis Theran (St Andrews)
Generic global and universal rigidity and the power of SDP for graph realisation
Thursday 01 June 2017,   16:00,   M240
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Parinya Chalermsook (Aalto CS)
Towards Fine-grained Combinatorial Optimization for NP-hard Problems
Thursday 01 June 2017,   14:45,   M240
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Camilla Hollanti (Aalto MATH)
Private information retrieval from coded databases
Thursday 01 June 2017,   14:00,   M240
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Aristides Gionis (Aalto CS)
Aligning networks: many and actively
Thursday 01 June 2017,   13:00,   M240
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Chris Brzuska
Foundations of cryptography and their applications
Tuesday 30 May 2017,   13:30,   T5, CS building

Chris Brzuska
Meet-in-the-middle attack
Tuesday 30 May 2017,   09:00,   M1 (M232)

Nico Döttling
Powerful Primitives for Weak Assumptions
Monday 29 May 2017,   13:30,   T2, CS building

Nico Döttling
Meet-in-the-middle attack
Monday 29 May 2017,   09:00,   M1 (M232)

Arnab Roy
Secure and Efficient Symmetric-key Primities for Multiparty Computation/Zero-Knowledge/Verifiable Computational
Wednesday 24 May 2017,   13:30,   T5, CS building

Smiljana Jaksic (University of Belgrade, Serbia)
Spaces of ultradistributions with applications to pseudo-differential operators
Wednesday 24 May 2017,   12:15,   M3 (M234)
This talk is based on joint works with Stevan Pilipovic and Bojan Prangoski. The first part of the talk is devoted to spaces of test functions and ultradistributions on the positive orthant of the Euclidean space, which can be described as analogous to the Gelfand-Shilov spaces and their dual spaces. Such ultradistributions are characterized through the Laguerre expansions. Furthermore, the full topological description of the spaces is given. The second part is devoted to the class of the Weyl pseudo-differential operators with radial symbols from the ultradistribution spaces. The continuity properties of these classes of pseudo-differential operators over the Gelfand-Shilov spaces and their dual spaces are proved. In this way, the classes of the Weyl pseudo-differential operators are extended to those with the radial symbols with the exponential and sub-exponential growth rate.
Seminar on analysis and geometry

Kai Virtanen
Solving Dynamic Optimization Problems
Wednesday 24 May 2017,   10:30,   M2 (M233)
Teaching demonstration

Arnab Roy
Meet-in-the-middle attack
Wednesday 24 May 2017,   09:00,   M1 (M232)

Prof. Samuli Siltanen (University of Helsinki)
Electrical impedance tomography imaging of stroke
Tuesday 23 May 2017,   14:15,   M3 (M234)
Seminar on Applied Mathematics

Vincent Grosso
Cryptographic implementations and physical defaults
Tuesday 23 May 2017,   13:30,   T2, CS building

Vincent Grosso
Meet-in-the-middle attack
Tuesday 23 May 2017,   09:00,   M1 (M232)

Esa Hyytiä (University of Iceland)
TBA
Monday 22 May 2017,   17:30,   M1 (M232)

Sergei Chubanov (University of Siegen)
TBA
Monday 22 May 2017,   16:45,   M1 (M232)

Pierre Nyquist (KTH)
TBA
Monday 22 May 2017,   16:00,   M1 (M232)

Sergei Chubanov (University of Siegen)
Optimality conditions for unconstrained convex optimization
Monday 22 May 2017,   10:00,   M1 (M232)

Esa Hyytiä (University of Iceland)
Routing jobs to servers
Monday 22 May 2017,   09:30,   M1 (M232)

Pierre Nyquist (KTH)
Time series analysis, specifically (G)ARCH processes for financial time series
Monday 22 May 2017,   09:00,   M1 (M232)

Dimitrios Ntalampekos (UCLA)
Uniformization of Sierpinski carpets by square carpets
Friday 19 May 2017,   14:15,   M3 (M234)
Uniformization of metric spaces is the problem of finding conditions on a metric space, under which it can be transformed to a canonical space, by a map that preserves the geometry. In this talk, our metric space will be planar Sierpinski carpets, and the canonical spaces are square Sierpinksi carpets. We prove that every Sierpinski carpet, under certain geometric assumptions, can be mapped by a quasisymmetric map to a square carpet. This is achieved with the aid of carpet-harmonic functions, which is a discrete notion of harmonic functions on Sierpinski carpets.
Harmonic analysis and PDE seminar

Prof. Daina Taimina (Cornell University)
Study mathematics and ... become an artist?
Tuesday 16 May 2017,   15:00,   C-hall (Y205)
When I was in middle school I was a good student and had very good grades in all subjects...except in art class where I was struggling to draw the way my teacher thought was the right way. I accepted my teacher's judgement that I can do anything but art and went to study mathematics. Could I imagine that some fifty years later I will be known as an artist? Mathematics and art are not too distant. In my talk, I will discuss the interplay between mathematics and art from my own perspective.
Joint Mathematics and Arts and Women in Mathematics Colloquium / Kirsi Peltonen

Céline Blondeau
Statistical attacks on symmetric cryptographic primitives (Job talk for Tenure Track in Cryptology position)
Friday 12 May 2017,   14:00,   T2, CS building

Céline Blondeau
Meet-in-the-middle attack (Teaching demonstration for Tenure Track in Cryptology position)
Friday 12 May 2017,   09:00,   M1 (M232)

Dissertation
Amaro Barreal
Doctoral thesis defense: Lattice codes for physical layer communications
Thursday 11 May 2017,   14:00,   M1 (M232)
Opponent Prof. Bharath Sethuraman, custos Camilla Hollanti.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Thomas Westerbäck
Combinatorial coding theory via polymatroids
Wednesday 10 May 2017,   16:15,   M3 (M234)
Matroid theory can be used to analyze many interesting properties of linear codes over finite fields. Recent research has proven matroid theory to be a valuable tool in several areas in coding theory, e.g. in distributed storage, index coding and network coding. Polymatroids, a generalization of matroids, can be associated with any finite code. In this talk I will present how polymatroids and codes are closely related via entropy and how polymatroid theory can be used in order to analyze many interesting properties of codes. New coding theoretical results will be given in the setting of polymatroids. These results can therefore also be applied to non-code objects that are associated with polymatroids.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Prof. Bharath Sethuraman (California State University, Northridge)
Matrices from Division Algebras and Fast Decodability (NOTE: ON TUESDAY!)
Tuesday 09 May 2017,   15:15,   M2 (M233)
We call two matrices A and B in M_n(C) mutually orthogonal if AB* + BA*=0, where A* indicates the conjugate transpose of A. The situation where such matrices arise from the embedding of a division algebra over a number field into M_n(C) is particularly interesting in wireless communications, where the presence of such matrices leads to fast decodability. We describe fundamental limits on the number of families of matrices that are mutually orthogonal across the families, and limits on the number of matrices in each family. The limits are obtained by a mix of techniques from both linear algebra and the theory of Brauer groups of commutative rings.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Robert Krone (Queen's University)
Rigid boundary components of non-negative rank matrices
Tuesday 09 May 2017,   10:15,   M237
The non-negative rank of a matrix is useful for algebraic statistics, but difficult to compute. The set of matrices with rank and non-negative rank both equal to r forms a semi-algebraic, Zariski-dense subset of the variety of rank r matrices. Describing all the boundary components of this set can provide a membership test, and this was accomplished for rank 3 by Mond, Smith and van Straten. Using a slightly different approach, we describe some of the boundary components in the higher rank cases, particularly the set of matrices that have a “rigid” nonnegative decomposition.
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

President Tuula Teeri, CEO Tapio Koivu (Heureka)
Sensual Mathematics
Monday 08 May 2017,   18:00,   Heureka
Further information
Opening of the Exhibition Sensual Mathematics at Heureka
Kirsi Peltonen

Prof. David Rios Insua (ICMAT-CSIC and Royal Academy of Sciences, Spain)
Adversarial Risk Analysis: Concepts, Applications and Challenges
Tuesday 02 May 2017,   15:15,   M1 (M232)
Our focus will be on problems in which two or more agents confront (as in non-cooperative game theory) and the consequences that they receive are random (as in risk analysis) and depend on the actions of all participants (as in game theory). This is motivated by problems in relation with high-profile terrorist attacks, business decision making and cyber-security. Most authors in this context would use game theoretical methods based on variants of Nash equilibria concepts. However, this is not always satisfactory in most of the above applications since beliefs and preferences of adversaries will not be readily available, frequently violating game theoretic common knowledge assumptions. In contrast, we focus on Adversarial Risk Analysis (ARA), an emergent paradigm for the type of problems we consider. ARA provides one-sided prescriptive support to a DM, maximizing her subjective expected utility, treating the adversaries' decisions as random variables. ARA models the adversaries' decision-making problems and, under assumptions about their rationality, tries to assess their beliefs and preferences. Then, ARA can predict their optimal actions. However, the uncertainty about the adversaries' judgements is propagated into their decisions, leading to random optimal adversarial decisions which provide the necessary distributions over the adversaries' decision. The main goals of ARA are to weaken standard common knowledge assumptions and provide more flexible models for opponent behavior. ARA is explicitly Bayesian in that subjective distributions are employed to express the uncertainties of the analyst. We shall outline basic concepts in ARA, some relevant applications and identify a few challenges.
Colloquium of Mathematics and Systems Analysis

Pekka Lehtelä
On the regularity of supersolutions to the porous medium equation
Friday 28 April 2017,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Tommi Brander, University of Jyväskylä
Detecting inclusions in Calderón's problem for p-Laplacian
Thursday 27 April 2017,   14:15,   M3 (M234)
Seminar in Applied Mathematics

Dr. David Cushing (Durham)
Bakry-Emery curvature functions of graphs
Wednesday 26 April 2017,   15:15,   M3 (M234)
Ricci curvature has proven to be a vital notion in many areas of mathematics. There have been various attempts at generalising this notion to graphs. We look at one such notion due to Bakry and Emery. We introduce the Bakry-Emery curvature function and obtain results on Cartesian products of graphs and also on a certain regularity property. I will also demonstrate interactive software that computes curvature.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Prof. Harri Ehtamo (Aalto)
Evoluutiopelit evakuointimalleissa - Pelastettavien kovan leikin peliteoreettinen kuvaus
Wednesday 26 April 2017,   15:00,   U8
LUMA-luennot lukiolaisille / Kangaslampi

Stavros Evdoridis (Aalto)
On Geometric Properties of Polyharmonic Mappings
Wednesday 26 April 2017,   12:15,   M3 (M234)
Seminar on analysis and geometry

Thomas Britz (UNSW Sydney)
A Nice Proof of Wei's Duality Theorem
Tuesday 25 April 2017,   15:15,   M1 (M232)
The Tutte polynomial was once an esoteric object known only to the then small community of combinatorialists. That changed when Greene (1976) pointed out the connection between this polynomial and weight enumerators, and how that connection provided a beautifully simple proof of the MacWilliams Identity (MacWilliams 1963) of coding theory fame. The Tutte polynomial is now of wide interest and appeal to the broader mathematical community who have found it lurking disguised in numerous areas of mathematics. Despite its present prominence, few are aware of how the Tutte polynomial provides another beautifully simple proof of a second celebrated duality theorem from coding theory, namely Wei’s Duality Theorem (Wei 1991). This proof, due to Duursma (2004), deserves better exposure, so this talk will present Duursma’s proof.
Colloquium of Mathematics and Systems Analysis

Prof. Kari Astala (University of Helsinki)
Self-similar sets (Teaching Demonstration for adjunct professor position)
Tuesday 25 April 2017,   14:15,   M1 (M232)

Elina Numminen (University of Helsinki)
The epidemics of a wild plant pathogen obey the laws of graph theory
Tuesday 25 April 2017,   10:15,   M237
The ecology and evolution of any pathogen is driven by the availability and dynamics of its host. For instance the surrounding landscape, and how it creates transmission barriers and highways can critically constrain the epidemiological dynamics. In my presentation, I will present analyses on a densely sampled longitudinal genomic dataset in order to assess the features driving spatio-temporal diversity and transmission dynamics of an obligate fungal plant pathogen, Podosphaera plantaginis in the Åland archipelago, the natural patchy metapopulation it occurs in. I utilize modern statistical inference techniques and mathematical graph theory to assess how different landscape features, especially roads impact the spread of this wind-dispersing pathogen and how this results in what seems at first as cryptic patterns of pathogen diversity. Our results show a prime example of analysing epidemics with the help of network concepts, an approach which often is tempting, yet inplausible due to lack of knowledge on the transmission network.
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Prof. Daniele Boffi (Universitá di Pavia)
Finite elements for elliptic problems: a priori error estimates (Teaching demonstration for adjunct professor position)
Monday 24 April 2017,   11:00,   M2 (M233)

Casimir Lindfors PERUTTU CANCELLED

Friday 21 April 2017,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Axel Målqvist, Chalmers University of Technology
Localization of elliptic multiscale problems
Thursday 20 April 2017,   10:00,   M2 (M233)
Seminar in Applied Mathematics

Prof. Samuli Siltanen (University of Helsinki)
Electrical impedance tomography imaging via the Radon transform
Wednesday 19 April 2017,   12:15,   M3 (M234)
Seminar on analysis and geometry

Ville Tengvall (University of Jyväskylä)
A Sobolev homeomorphism that cannot be approximated by diffeomorphisms in $W^{1,p}$
Wednesday 12 April 2017,   12:15,   M3 (M234)
Joint work with Daniel Campbell and Stanislav Hencl
Seminar on analysis and geometry

Liam Solus (KTH)
Learning Bayesian Networks via Edge Walks on DAG Associahedra
Tuesday 11 April 2017,   10:15,   M237
The focus of this talk will be an application of convex polytopes to causal inference. Graphical models based on directed acyclic graphs (DAGs), also known as Bayesian networks, are used to model complex cause-and-effect systems across a vast number of research areas including computational biology, epidemiology, sociology, and environmental management. A DAG model is family of joint probability distributions over the nodes of a DAG G that entail a set of conditional independence (CI) relations encoded by the nonedges of G. A fundamental problem in causality is to learn an unknown DAG G based only on a set of observed conditional independence relations. Since multiple DAGs can encode the same set of CI relations, a property termed Markov equivalence, the goal is to identify efficient algorithms that consistently recover a DAG within the correct Markov equivalence class. We will describe a pair of greedy algorithms for DAG model selection that operate via edge walks on a family of generalized permutohedra called DAG associahedra. We will present consistency guarantees for these algorithms, and compare them with the more classical approaches to Bayesian model selection in both efficiency and strength of satisfied identifiability assumptions. To better understand the efficiency of these new algorithms, we study two new generating functions associated to a graph which share rich connections with classic combinatorial structures.
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Juulia Happonen
Theory Behind Regulatory Capital Formulae
Monday 10 April 2017,   15:15,   M2 (M233)

Matias Vestberg
Up to Your Neck in Shallow Water
Friday 31 March 2017,   14:15,   M3 (M234)
We take a plunge into the world of shallow water dynamics as described by the diffusive wave approximation. This nonlinear parabolic PDE is studied using De Giorgi and Moser type iteration techniques to obtain local boundedness of weak solutions. We also present fundamental solutions in the flat case and make some remarks regarding the existence of solutions.
Harmonic analysis and PDE seminar

Matthew Romney (University of Illinois)
Existence of quasiconformal parametrizations of metric surfaces with improved dilatation
Wednesday 29 March 2017,   12:15,   M3 (M234)
The measurable Riemann mapping theorem is the fundamental existence theorem for homeomorphic solutions to the Beltrami equation in the plane, i.e. quasiconformal mappings, and shows the flexibility of such mappings. More particularly, it gives hope for a positive answer to this question: given a metric space (X,d) quasiconformally homeomorphic to a simply connected domain in the complex plane, can one find a quasiconformal mapping from X onto the same domain which improves the dilatation to within a fixed universal bound? If so, what it the sharp value? This talk will discuss a solution of this problem.
Seminar on analysis and geometry

Christian Haase (Freie Universität Berlin)
Finiteness Theorems for Lattice Polytopes
Tuesday 28 March 2017,   15:15,   M1 (M232)
A lattice polytope is the convex hull of finitely many points all whose coordinates are integers. These fundamental geometric objects appear in a variety of mathematical fields like combinatorics or algebraic and symplectic geometry, with applications ranging from optimization to statistics to mathematical physics in string theory. Considerable effort has gone into several classification projects for classes of lattice polytopes. All these classifications are based on theorems, stating that the class under consideration has only finitely many elements, or at least that certain parameters are bounded in the class. In this talk, I will give an overview of my favorite finiteness theorems, starting in the 19th century with Pick and Minkowski and ending with recent developments to be published in 2017+.
Colloquium of Mathematics and Systems Analysis

Johan Wästlund (Chalmers University of Technology)
Optimization Through Games
Tuesday 28 March 2017,   10:15,   M237
Further information
I will discuss a couple of different methods for analyzing optimization problems on large random structures. In particular I will show how some results can be derived by inventing two-person games whose optimal strategies encode the solution to problems like minimum weight matching on weighted graphs.
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

Matthias Grezet
Rank distribution and generalized weights of Delsarte codes
Wednesday 22 March 2017,   15:15,   M3 (M234)
Delsarte codes and, in particular, all rank-metric codes play an important role in network coding to correct errors and secure an adversarial channel. The purpose of this talk is to study the properties inherent to Delsarte codes via algebraic and combinatoric methods. We will first present an analogue of the Singleton bound theorem for this context. Then, we will talk about the rank distribution of a specific code. Finally, we will introduce a new invariant, called the set of generalized weights, and see how it can characterize different type of codes
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Mikko Stenlund (University of Jyväskylä)
Stein's method for dynamical systems
Wednesday 22 March 2017,   12:15,   M3 (M234)
We present an adaptation of Stein’s method of normal approximation to the study of dynamical systems. The method yields a convergence rate essentially with the same amount of work as the central limit theorem, together with a multiplicative constant that can be computed directly from the assumptions.
Seminar on analysis and geometry

Estibalitz Durand Cartagena (UNED, Spain)
∞-harmonic functions on metric measure spaces
Friday 17 March 2017,   15:00,   M3 (M234)
Harmonic analysis and PDE seminar

Prof. Henry Segerman (Oklahoma State University)
3D Shadows: Casting Light on the Fourth Dimension
Thursday 16 March 2017,   18:30,   Heureka
Our brains have evolved in a three-dimensional environment, and so we are very good at visualising two- and three-dimensional objects. But what about four-dimensional objects? The best we can really do is to look at three-dimensional "shadows". Just as a shadow of a three-dimensional object squishes it into the two-dimensional plane, we can squish a four-dimensional shape into three-dimensional space, where we can then make a sculpture of it. If the four-dimensional object isn't too complicated and we choose a good way to squish it, then we can get a very good sense of what it is like. We will explore the sphere in four-dimensional space, the four-dimensional polytopes (which are the four-dimensional versions of the three-dimensional polyhedra), and various 3D printed sculptures, puzzles, and virtual reality experiences that have come from thinking about these things. I talk about these topics and much more in my new book, "Visualizing Mathematics with 3D Printing".
Mathematics and Arts Colloquium / Kirsi Peltonen

Prof. Henry Segerman (Oklahoma State University)
"Design of 3D printed mathematical art"
Wednesday 15 March 2017,   16:00,   B-Hall
When visualising topological objects via 3D printing, we need a three-dimensional geometric representation of the object. There are approximately three broad strategies for doing this: "Manual" - using whatever design software is available to build the object by hand; "Parametric/Implicit" - generating the desired geometry using a parametrisation or implicit description of the object; and "Iterative" - numerically solving an optimisation problem. The manual strategy is unlikely to produce good results unless the subject is very simple. In general, if there is a reasonably canonical geometric structure on the topological object, then we hope to be able to produce a parametrisation of it. However, in many cases this seems to be impossible and some form of iterative method is the best we can do. I will discuss these matters with many examples, including visualisation of four-dimensional polytopes (using orthogonal versus stereographic projection) and Seifert surfaces (comparing my work with Saul Schleimer with Jack van Wijk's iterative techniques). I will also describe some computational problems that have come up in my 3D printed work, including the design of 3D printed mobiles (joint work with Marco Mahler), "Triple gear" and a visualisation of the Klein Quartic (joint work with Saul Schleimer), and hinged surfaces with negative curvature (joint work with Geoffrey Irving).
Mathematics and Arts Colloquium / Kirsi Peltonen

Taoufiq Damir
The bounded gaps between primes (NOTE unusual time!)
Wednesday 15 March 2017,   14:15,   M3 (M234)
The aim of the talk is to present a survey on the main ideas developed by Selberg, Goldston, Pintz, Yildirim, Maynard and Tao in order to prove the bounded gap between primes, namely the existence of infinitely many primes p such that p+M is prime, where M is some positive even integer. The talk will be in two parts. The first part will be mostly dedicated to an introduction to elementary Analytic number theory and Sieve theory, then in the second part we will sketch the proofs of the main results leading to the bounded gaps.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Eero Ruosteenoja (University of Jyväskylä)
Tug-of-war games
Wednesday 15 March 2017,   12:15,   M3 (M234)
Ten years ago Peres, Schramm, Sheffield and Wilson introduced two-player zero-sum stochastic games that they called tug-of-war games. They showed that these games have close connections to certain nonlinear PDEs of p-Laplacian and infinity Laplacian type. I will give an overview of the topic. No background knowledge of probability theory is needed.
Seminar on analysis and geometry

Petteri Kaski
Directed Hamiltonicity and Generalized Laplacians
Tuesday 14 March 2017,   10:15,   M237
The (symbolic) Laplacian matrix of a graph G is a rich source of algebraic combinatorics. Our interest is on directed graphs, where by puncturing the Laplacian at a vertex r and taking the determinant, we obtain, by the classical (directed) Matrix–Tree Theorem, a symbolic generating function for the spanning out-branchings of G rooted at r. In this talk we seek to understand Laplacian determinants via the algebraic combinatorics of “incidence assignments” that we can then turn into new randomized algorithm designs for, e.g., the Hamiltonian cycle problem on directed graphs. We present two such algorithm designs. First, for any constant 0 < \lambda < 1 and any prime p, we present a randomized algorithm that, given an n-vertex directed graph G as input, counts the number of Hamiltonian cycles modulo p^{\lfloor(1-\lambda)n/(3p)\rfloor} in expected time c^n for a constant c<2 that depends only on p and \lambda. Second, we present a randomized algorithm that with a negligible probability of a false negative detects a directed Hamiltonian cycle in a given n-vertex directed graph G in time O*(3^{n-\alpha(G)}) and space polynomial in n, where \alpha(G) is the size of a maximum independent set in G. This is joint work with Andreas Björklund (Lund University) and Ioannis Koutis (University of Puerto Rico).
ASci Large Structures Seminar / Freij-Hollanti, Kubjas

Jonas Tölle
The p-Laplace evolution equation as p tends to 1: Mosco convergence and convergence of solutions
Friday 10 March 2017,   14:15,   M3 (M234)
Harmonic analysis and PDE seminar

Casimir Lindfors
Regularity for nonlinear parabolic PDEs with general growth
Thursday 09 March 2017,   15:40,   M3 (M234)
Doctoral student talk / Engström

Pekka Lehtelä
Generalized solutions to the porous medium equation
Thursday 09 March 2017,   15:15,   M3 (M234)
Doctoral student talk / Engström

Hoa Ngo
Information spreading in large networks
Thursday 09 March 2017,   14:40,   M3 (M234)
Doctoral student talk / Engström

Armando Gutiérrez
The horoboundary of metric spaces and its role in dynamics
Thursday 09 March 2017,   14:15,   M3 (M234)
Doctoral student talk / Engström

Juho Andelmin
Solving the green vehicle routing problem and allocating resources based on efficiency analysis
Thursday 09 March 2017,   13:40,   M3 (M234)
Doctoral student talk / Engström

Yrjänä Hynninen
Mathematical methods for medical decision making
Thursday 09 March 2017,   13:15,   M3 (M234)
Doctoral student talk / Engström

Anton von Schantz
Modeling crowd dynamics in an evacuation as a multiagent system
Thursday 09 March 2017,   11:40,   M205
Doctoral student talk / Engström

Heikki Puustinen
Network optimization and simulation in military air mission planning
Thursday 09 March 2017,   11:15,   M205
Doctoral student talk / Engström

Pekka Laitila
Facilitating expert elicitation of probabilities for Bayesian networks
Thursday 09 March 2017,   10:40,   M205
Doctoral student talk / Engström

Mikko Harju
Spatial decision analysis with incomplete information
Thursday 09 March 2017,   10:15,   M205
Doctoral student talk / Engström

Tom Gustafsson
Numerical methods for lubrication and elastic contact
Wednesday 08 March 2017,   16:40,   M205
Doctoral student talk / Engström

Mikael Laaksonen
Spectral inverse iteration for stochastic eigenvalue problems
Wednesday 08 March 2017,   16:15,   M205
Doctoral student talk / Engström

Lauri Mustonen
Surrogate models and computational inverse problems
Wednesday 08 March 2017,   15:40,   M205
Doctoral student talk / Engström

Vesa Kaarnioja
On the structure and eigenvalues of lattice-theoretic tensors
Wednesday 08 March 2017,   15:15,   M205
Doctoral student talk / Engström

Anna-Lena Horlemann-Trautmann
Symbol Erasures in Random Network Coding
Wednesday 08 March 2017,   15:15,   M3 (M234)
In random network coding we want to communicate over a noisy network channel with one sender and several receivers, where all receivers want to get the same information from the sender. We encode the data before sending it through the network, so the receivers can reconstruct the original data from the corrupted data. From a mathematical point of view, classical tools used in this context are projective spaces over finite fields. In this talk we will give an introduction to random network coding and explain how the classical model by Kötter and Kschischang treats erasures during the communication. Then we give an alternative model and show that, depending on the network topology, the classical or the alternative model can be advantageous for erasure correction.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Prof. Kaie Kubjas (Aalto)
Matrices, photos and Netflix
Wednesday 08 March 2017,   15:00,   TU1
LUMA-luennot lukiolaisille / Kangaslampi

Juha Kuortti
Spectral characteristics of the vocal tract
Wednesday 08 March 2017,   14:40,   M205
Doctoral student talk / Engström

Diana Apetrei
Advances in multicentric calculus
Tuesday 07 March 2017,   16:40,   M203
Doctoral student talk / Engström

Tiina Vesanen
Numerical aspects of multicentric calculus
Tuesday 07 March 2017,   16:15,   M203
Doctoral student talk / Engström

Antti Ojalammi
On exterior acoustics and speech modelling
Tuesday 07 March 2017,   15:40,   M203
Doctoral student talk / Engström

Ferdinand Blomqvist
The closest vector problem in high dimension
Tuesday 07 March 2017,   15:15,   M203
Doctoral student talk / Engström

Lauri Perkkiö
Differential material parameter in finite element analysis
Tuesday 07 March 2017,   10:40,   M205
Doctoral student talk / Engström

Amaro Barreal
Lattices for physical layer network coding
Tuesday 07 March 2017,   10:15,   M205
Doctoral student talk / Engström

Prof. Petteri Kaski
Arithmetic circuits for multilinear tasks (45min, NOTE unusual time!)
Wednesday 01 March 2017,   17:15,   M3 (M234)
This talk will give a brief introduction to the design of arithmetic circuits for solving computational tasks, with a focus on multilinear tasks and designs, such as fast matrix multiplication and fast polynomial multiplication in the bilinear case, and higher-order designs such as determinants, permanents, and our recent design (with Andreas Björklund) for the \binom{6}{2}-linear form, which e.g. captures the task of counting the 6-cliques in a given graph.
ANTA Seminar: Algebra, Number Theory, and Applications to Communications and Computing / Karpuk, Kaski, Hollanti, Greferath

Clifford Gilmore (University of Helsinki)
Growth rates of frequently hypercyclic harmonic functions
Wednesday 01 March 2017,   12:15,   M3 (M234)
The notion of frequent hypercyclicity stems from ergodic theory and has been an active area of research since it was introduced by Bayart and Grivaux (2004). Many natural bounded linear operators are frequently hypercyclic, for instance the differentiation operator on the space of entire functions. We will begin by recalling some basic examples and the pertinent notions of frequent hypercyclicity. We then consider the partial differentiation operator acting on the space of harmonic functions on R^n. Our primary goal is to identify sharp growth rates, in terms of the L^2-norm, of harmonic functions that are frequently hypercyclic vectors for the basic partial differentiation operator. This answers a question posed by Blasco et al. (2010). This is joint work with Eero Saksman and Hans-Olav Tylli.
Seminar on analysis and geometry

Eero Saksman (University of Helsinki)
The Riemann zeta function meets Gaussian multiplicative chaos
Tuesday 28 February 2017,   15:15,   M1 (M232)
We begin by recalling some basic properties of the Riemann zeta function and its relevance to number theory. Later on we describe it's chaotic nature on the critical strip. The final theme to be discussed is the functional statistics of the zeta function on the critical line. The last mentioned topic is based on joint work with Christian Webb (Aalto).
Colloquium of Mathematics and Systems Analysis

Dario Gasbarra (University of Helsinki)
Estimating passengers travel lenghts distributions in Helsinki commuter trains
Tuesday 28 February 2017,   10:15,   M237
A local train stops at stations 0, 1, . . . , T and passengers getting in and out a wagon are counted at every station. Since passengers are not labeled and with the same ticket it is possible to travel across all the line, when a passenger gets off the train, it is not known from which station he started. The distribution of the individual trips satisfies a constrained system of linear diophanitine equations, which typically is underdetermined. Nevertheless we show that, when i.i.d. realizations are collected , the probability distribution of the travel lengths, depending on the passenger’s departure station is identifiable. We use a Bayesian data augmentation, where the the distribution of the individual trips is the hidden variable. The posterior distribution is explored by the fiber walk Markov chain Monte introduced by Diaconis and Sturmfels 1998.
AScI Large Structures Seminar / Freij-Hollanti, Kubjas

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