# Contributed Talks

## Tentative Schedule

Session 1 (Thursday, 27 September 2018)

**11:30**Russ Woodroofe: The story of a figure**12:00**Alba Marina Málaga Sabogal: Tools for 3D printing mathematical surfaces**12:30**Mirza Krbezlija: Using Java and the CPLEX solver for solving integer linear programs

Chair: Matjaž Krnc

Problem Session (Thursday, 27 September 2018)

The problem session starts at **16:30**.

Chair: Eric Gottlieb

Session 2 (Friday, 28 September 2018)

**11:30**Matjaž Krnc: Pipelines in mathematical research**12:00**Alba Marina Málaga Sabogal: Reverse engineering your mathematical PDF files**12:30**Tomaž Pisanski: Computing Jacobian matrix of a graph with Sage and Python

Chair: Katja Berčič

Session 3 (Friday, 28 September 2018)

**16:30**Katja Berčič: Databases of discrete mathematical objects and*DiscreteZOO***17:00**Janoš Vidali:*DiscreteZOO*– a repository of combinatorial objects and its companion Sage package

Chair: Nino Bašić

## Abstracts

**Databases of discrete mathematical objects and DiscreteZOO**

Katja Berčič

Universidad Nacional Autónoma de México, Morelia, Mexico

**Abstract:** There are (at least) two interesting problems when it comes to databases of mathematical objects. On one hand, they should be useful to a researcher who wants to look up properties or references or to a researcher who is looking for a pattern or a counterexample. On the other hand, a typical researcher who produces a collection of objects, say graphs, does not have the resources to develop a platform such as The On-Line Encyclopedia of Integer Sequences or The L-functions and Modular Forms Database. One of the objectives of the *DiscreteZOO* project is to provide a reusable platform for databases of mathematical objects.

I will talk about how *DiscreteZOO* fits into the larger effort on managing mathematical knowledge, what problems one encounters in making a reusable platform for databases of mathematical objects and the current work on a database of maniplexes.

**Using Java and the CPLEX solver for solving integer linear programs**

Mirza Krbezlija

University of Primorska, Koper, Slovenia

**Abstract:** In my final project paper for the first bologna cycle, among other things, I studied the vector connectivity problem. Vector connectivity is a graph optimization problem whose optimal value can be computed by formulating it as an integer linear program. To solve the integer linear program and to find its optimal value I used the programming language Java together with the CPLEX solver library. I will present some difficulties I had while using both Java and the CPLEX solver together with the adjustments I had to do in order to get past those difficulties so I could obtain the desired results for the related topic.

**Pipelines in mathematical research**

Matjaž Krnc

University of Primorska, Koper, Slovenia

**Abstract: **In this talk we will go through several hands-on examples of my research projects where the CoCalc service was used extensively. We will discuss the benefits and drawbacks of the tools offered by the service. The emphasis will be on the pipelining several tools covered in our workshop, and gluing them together as needed.

**Reverse engineering your mathematical PDF files**

Alba Marina Málaga Sabogal

French Institute for Research in Computer Science and Automation, Paris, France

**Abstract:** How many times have you realized that you lost your LaTeX source files for that beautiful PDF paper? How many times did you needed to quote some formula from a paper and you had to type it all again by yourself? If you are a sighted person, you may want to recover LaTeX sources for convenience. But if you are a blind person, having access to a document with rich markup may be essential for your screen reader to understand the content of the document. That's what accessibility is about: to make easy for the helpful technology to work correctly.

In the project OPALINe we work on making electronic documents accessible again. Our main tool for that is the GROBID library. In this talk I will explain how to use GROBID together with the im2markup visual formula decompiler in order to get back a source file for a mathematical paper PDF.

**Tools for 3D printing mathematical surfaces**

Alba Marina Málaga Sabogal

French Institute for Research in Computer Science and Automation, Paris, France

**Abstract:** In this talk I will present a few software tools that you can use for 3D printing mathematical surfaces, like real algebraic surfaces, invariant surfaces in dynamics or minimal surfaces. Personnally the tools I use the most often are MathMod and Blender, but during the talk I will also present Functy, Surface Evolver, Antimony, Bertini_real, NetFabb and others.

**Computing Jacobian matrix of a graph with Sage and Python**

Tomaž Pisanski

University of Primorska, Koper, Slovenia & IMFM, Ljubljana, Slovenia

**Abstract:** We present the power of Sage and Python by exhibiting a short program for computing the Jacobian group of a graph.

Here is the program:

def Jacobian(g, verbose=False): if verbose: g.show() lm = g.laplacian_matrix() A = matrix(ZZ, lm) AS = A.smith_form() diag = AS[0].diagonal() res = [] for x in diag: if x > 1: res.append(x) return res

Using the above program one can easily compute the number of spanning trees of a connected graph.

*DiscreteZOO* – a repository of combinatorial objects and its companion Sage package

Janoš Vidali

University of Ljubljana, Ljubljana, Slovenia

**Abstract:** *DiscreteZOO* is a project combining a central repository of discrete objects, its website front-end and extensions for software packages like Sage. The repository contains certain precomputed properties to speed up the processes of filtering, searching and computation. For now, it can store graphs, with the groundwork already laid out for more combinatorial objects (such as maps, maniplexes, geometries, etc.).

In the talk we will show how one can interact with *DiscreteZOO* on the example of the censuses of vertex-transitive graphs by Royle, Conder, and Potočnik, Spiga & Verret. We will perform some example searches on the website, download a subset of the database and showcase some queries that can be run locally with the Sage package.

**The story of a figure**

Russ Woodroofe

University of Primorska, Koper, Slovenia

**Abstract:** I'll describe how I drew a complex figure for a recent paper.