Thesis presentation in Master of Applied Statistics (MAS)

### Guðmundur Helgason

Titill: Hversu lengi þarf ég að bíða? Forspárlíkön fyrir biðtíma í þjónustuveri CCP

Location: V-157, VRII

Time: Thursday 1. June at14:00.

### Abstrat:

Í þessari rannsókn, með hjálp ýmissa tölfræðiaðferða, spáum við fyrir um biðtíma eftir svari við tölvupósti með gögnum frá þjónustuveri CCP, framleiðanda tölvuleiksins EVE Online. Að mestu leyti er notast við tvíkosta tölfræðilíkön þar sem spáð er fyrir um hvort að svar sé gefið fyrir ákveðinn tímapunkt eða ekki. Samfelldar aðferðir eru þó einnig notaðar, bæði til að spá fyrir um biðtíma í sjálfu sér og hvort svar sé gefið fyrir ákveðinn tíma eða ekki. Auk greiningarlegra aðferða til forspáar er einnig notast við einfaldari empírískar aðferðir til að meta dreifingu biðtíma og líkindi á svari eftir ákveðinn tíma. Tiltækar rannsóknir á sviði þjónustuvera, gæða í þjónustu, áhrifa þess að bíða eftir þjónustu og aðferða sem notast hefur verið við til að spá fyrir um biðtíma eru skoðaðar. Aðferðirnar sem notast var við til biðtíma forspáar eru bornar saman, kostir þeirra og gallar ræddir, auk hugsanlegra hagnýtra eiginleika.

Leiðbeinendur:

Anna Helga Jónsdóttir

Matthías Kormáksson

Prófdómari: Thor Aspelund

http://www.hi.is/vidburdir/meistarafyrirlestur_hversu_lengi_tharf_eg_ad_bida_forsparlikon_fyrir_bidtima_i_thjonustuveri_ccp

Thesis presentation in Master of Applied Statistics (MAS)

### Stella Kristín Hallgrímsdóttir

Title: Samband veðurs og komufjölda á bráðamóttökur Landspítala

Location: V-157, VRII

Time: Monday 29. May at 14:00.

### Abstract:

The objective of this project is to study the seasonal and weekly fluctuations in number of arrivals to the emergency departments of the University Hospital of Iceland and also to assess the influence of weather on the number of arrivals. Four emergency departments were examined; the Emergency Department in Fossvogur, the Emergency Unit in the Children‘s Hospital Department, Hjartagátt which is the emergency department for people with suspected acute heart problems, and the Psychiatry Emergency Department. The weather variables that were mostly looked into are temperature, wind speed, precipitation and cloudiness. Seasonal fluctuations were modeled with sine and cosine waves and with the help of linear regression a new variable was made that describes the seasonal fluctuations and linear increase in the number of arrivals. A few ARIMA models were built to predict the number of arrivals in the Emergency Department in Fossvogur and in the Children‘s Emergency Department. The models were compared to find the best prediction model for each department. To assess whether weather affects the number of arrivals in the emergency departments, the weather variables were added one by one to the best prediction model for each department to see if the model‘s prediction root-mean squared error (RMSE) decreases when information about weather is added to the model. Principal components analysis was also used to combine the weather variables into fewer new variables. The new variables were then added to the ARIMA models to assess their effect on the goodness of the models. The results show that adding the weather information slightly decreases prediction RMSE in the Emergency Department in Fossvogur but increases it for the Children‘s Emergency Department. That both applies to when each weather variable was looked into separately and when the principal components were used. Therefore, it can be concluded that weather does not affect the number of arrivals to the Children‘s Emergency Department but it has a minor effect on the number of arrivals to the Emergency Department in Fossvogur. Furthermore, the results show that a good prediction model for the number of arrivals to the emergency departments can be developed only using calendar variables.

Advisors: Dr. Sigrún Helga Lund and Dr. Tryggvi Helgason

Examiner: Dr. Ólafur Pétur Pálsson

http://www.hi.is/vidburdir/meistarafyrirlestur_samband_vedurs_og_komufjolda_a_bradamottokur_landspitala

Math Colloquium

### Speaker: Valentina Giangreco, University of Iceland

### Title: Non-analyticity of holographic Rényi entropy in Lovelock gravity

Location: Tg-227 (Tæknigarður, 2. hæð)

Time: Friday 26 May at 13:20

### Abstract:

In the first part of my talk I will introduce the definition of Rényi entropy, and some basic concepts of the so-called holographic principle (AdS/CFT). The second part of the talk is devoted to the analysis of certain black hole instabilities in gravity theories with higher derivative corrections (Lovelock gravity theories) and their implications for the holographic Rényi entropy.

Math Colloquium

### Speaker: Ayan Mukhopadhyay, Vienna University of Technology

### Title: The mogul pistes of non-equilibrium causal correlations in strongly interacting holographic systems: universal features and how they reveal the microscopic theory.

Location: V-158 (VR-II)

Time: Thursday 11 May at 13:30

### Abstract:

I will report exact calculations of holographic retarded (causal) correlation function away from equilibrium in states driven from one thermal equilibrium to another by a homogeneous energy injection. Our calculations reveal universal features of thermalization of the retarded propagator. Furthermore, I will discuss how the measurement of the non-equilibrium retarded propagator (possible by techniques such as pump-probe spectroscopy) enables us to learn a lot about the dual gravity description (i.e. the microscopic theory) by establishing novel connections between quantum information content of non-equilibrium density matrices and the classical dynamics of the apparent and event horizons in the dual geometries.

Math Colloquium

### Speaker: Jason Smith, University of Strathclyde

### Title: Poset Fibrations and Their Applications to Pattern Posets

Location: Tg-227 (Tæknigarður, 2. hæð)

Time: Friday 21 April at 13:30

### Abstract:

A poset fibration is a rank and order preserving surjective map between posets. It was shown by Quillen that many properties of posets can be maintained across a fibration, we introduce some of these results. Pattern occurrence has been studied on a wide range of combinatorial objects, and using the notion of pattern containment we can define a poset on these objects. Many such pattern posets have been studied in the literature and the results on these posets often have a similar theme. Using poset fibrations we introduce some results that show why such similarities arise between different pattern posets.

Math Colloquium

### Speaker: Friðrik Freyr Gautason, K.U. Leuven

### Title: Large field inflation in string theory

Location: Tg-227 (Tæknigarður, 2. hæð)

Time: Friday 7 April at 13:20

### Abstract:

I start by motivating that certain questions in cosmology, in particular dark energy and large field inflation, should be addressed in a quantum model that includes gravity such as string theory. I will give an overview how these questions are translated to dynamics in the extra dimensions of string theory and what challenges one encounters. I then present a novel model for inflation in string theory and discuss some of the stringent consistency constraints the parameters of the model must satisfy and how these constraints affect cosmological observables.

Applications are invited for the full position of Research Specialist in Applied Mathematics at the Mathematics Division of the Science Institute, University of Iceland.

Continue reading 'Research Specialist in Applied Mathematics at the Science Institute, University of Iceland'»

Applications are invited for the full position of Research Scientist in Mathematics at the Mathematics Division of the Science Institute, University of Iceland.

Continue reading 'Research Specialist in Mathematics at the Science Institute, University of Iceland'»

Math Colloquium

### Speaker: Tom Steentjes, Eindhoven University of Technology

### Title: Feedback stabilization of nonlinear systems: “universal” constructions towards real-life applications

Location: Tg-227 (Tæknigarður, 2. hæð)

Time: Friday 17 March at 13:20

### Abstract:

Various feedback stabilizers based on Sontag’s “universal” formula for stabilizing control laws are presented, incorporating restrictions inspired by real-life applications. The first main contribution is an extension of Sontag’s “universal” formula for positive nonlinear control systems. More specifically, an auxiliary function is introduced in the feedback interconnection, such that invariance of the positive orthant is retained for the system in closed loop with the “universal” stabilizer. We further state a “universal” event-based stabilizer for bounded controls and develop an extension of the controller for positive systems. In a motivating case study from systems biology, the methodology is shown to provide clinically realistic control inputs, which can be used for treatment in real life. The second main contribution is the construction of continuous and piecewise affine (CPA) feedback stabilizers for nonlinear control systems affine in the input, motivated by the ease of implementation of the resulting control law. A verification procedure for “universal” CPA stabilizers is provided, together with an alternative computational method for CPA stabilizers via linear programming. Two numerical examples are presented for illustration of the CPA method.

Short bio:

Tom Steentjes was born in Tilburg, the Netherlands, in 1993. He received his BSc degree in Electrical Engineering (Automotive) in 2014, from the Department of Electrical Engineering at Eindhoven University of Technology (TU/e). In 2016, he completed the Systems and Control master’s program at the TU/e. The MSc thesis, entitled “Feedback stabilization of nonlinear systems: ‘universal’ constructions towards real-life applications”, was supervised by dr. Alina Doban and dr. Mircea Lazar. The MSc degree was granted with distinction Cum Laude.

Math Colloquium

### Speaker: Paolo Zanardi, University of Southern California

### Title: Quantum algorithms for topological and geometric analysis of Big Data

Location: V-138 (VR-II)

Time: Monday 20 February at 10:00

### Abstract:

Extracting useful information from large data sets can be a daunting task. Topological methods for analysing data sets provide a powerful technique for extracting such information. Persistent homology is a sophisticated tool for identifying topological features and for determining how such features persist as the data is viewed at different scales. I will discuss quantum machine learning algorithms for calculating Betti numbers – the numbers of connected components, holes and voids – in persistent homology, and for finding eigenvectors and eigenvalues of the combinatorial Laplacian. The algorithms provide an exponential speed-up over the best currently known classical algorithms for topological data analysis.

Reference: Seth Lloyd, Silvano Garnerone e Paolo Zanardi, Quantum algorithms for topological and geometric analysis of data, Nature Communications 7, 10138 (2016). See also: http://news.mit.edu/2016/quantum-approach-big-data-0125