2021 Spring Term Math Student Seminars
Welcome to Spring term. While we continue to play our part during the current COVID19 pandemic and social distancing, our inperson student seminars are still on hold, we are having a virtual Math Seminar for our students!
Coordinated by Union College Professors Louisa Catalano and Phanuel Mariano, and presented by:
Greg Malen, Union College, "HighDimensional Holeyominoes and Hyperbolic Polyforms"
A polyomino is a finite ``rookconnected'' subset of squares on an infinite chessboard, which one can imagine is constructed by taking individual square tiles and gluing them together along their edges. In this talk, I will be considering extremal properties of these structures with respect to the requirement that a fixed number of squares is arranged such that their edges bound a maximal number of holes. These ``holeyominoes'' tend towards beautiful symmetries and efficient geometric properties. Building on earlier results with squares in 2dimensional Euclidean space, I will present new asymptotic bounds for the maximum number of holes which can be bounded by $n$ $d$dimensional cubes in $d$dimensional Euclidean space. Furthermore, we will look at ongoing efforts to find similar results in the hyperbolic plane for subsets of a $\{p,q\}$tiling, where $q$ regular $p$gons meet at every vertex.
Date/time: Thursday, May 27th at 1:20pm2:15pm
Location: Zoom ID: https://union.zoom.us/j/92591304428
**************************************
Previous talks:
Mary Annese ACAS, CPCU, MAAA, to present “An Introduction to the Actuarial Profession”
An introduction to a promising career in what has been touted as one of the nation’s top ranked professions because of its employability, career growth, highpaying salaries, and worklife balance.
Date/time: Thursday, May 6th at 1:20pm2:15pm
Location: Zoom ID: https://union.zoom.us/j/92591304428
What you will learn:
 What an Actuary is
 What Actuaries do
 How to become an Actuary
 What the Casualty Actuarial Society is
 Why this is an attractive career
 Your next steps
Who should attend?
 Undergraduate students majoring in actuarial science, math, statistics, business, or other related fields
 Undecided undergraduate students with an interest in math, statistics, business, or other related fields.
 Go to: CASstudentcentral.org and register to become a student member. It’s free and provides you access to a wealth of tips, tools and resources.
Emily HoopesBoyd from Kent State University
Date/time: Thursday, April 15th at 1:20pm2:15pm
Location: Zoom ID: https://union.zoom.us/j/92591304428
Title: The Images of Polynomials Evaluated over Matrices
Abstract: A version of the L’vovKaplansky conjecture states that the image of a multilinear polynomial evaluated over matrices, with entries from the complex numbers, is a vector space. This statement has been proven only for the case of 2×2 matrices, but many partial results have been proven within the last decade. We will consider this problem in a slightly different context; rather than taking the matrix entries to be from the complex numbers, we will consider matrices over an algebraically closed skew field, which we will denote by $K$. We will show that the image of any multilinear polynomial with coefficients from $K$, evaluated over $M_m(K)$, is $M_m(K)$. We will also prove that any matrix in $M_m(K)$ may be written as the sum of three or fewer elements from the image of any generalized polynomial. In particular, the image of the polynomial $xyyx$ has some special properties over a variety of matrix rings, including the ring of matrices over the complex numbers.
Wednesday, January 29th
12:30pm pizza & beverages in Bailey 204
12:55pm Seminar will be in Bailey 207
Please see flyers posted in Bailey Hall for title and abstract
Friday, January 31st
4:00pm light refreshments in Bailey 204
4:15pm Seminar will be in Bailey 207
Please see flyers posted in Bailey Hall for title and abstract
Thursday, Jan 23rd
Making Our Mark, Women in Mathematics, at Union and Beyond
In conjunction with our celebration of the 50th anniversary of coeducation at Union College, we invite you all to a special celebration of women in mathematics in our upcoming math seminar. We will hear from Professor Susan Niefield about her experience as a mathematician and as the first woman who joined the math department faculty at Union. We will then briefly introduce some professional organizations that focus on making the mathematical community more inclusive. In particular, members of The Association for Women in Mathematics Chapter at Union will share their stories and talk about their events and resources. Finally, we will watch a short film "Journeys of Women in Mathematics", that shows the difficulties and triumphs of three women mathematicians from three different continents: Neela Nataraj from India, Aminatou Pecha from Cameroon, and Carolina Araujo from Brazil.
Thursday, January 16th  Union College welcomes:
Mary Annese ACAS, CPCU, MAAA,
to present “An Introduction to the Actuarial Profession”
An introduction to a promising career in what has been touted as one of the nation’s top ranked professions because of its employability, career growth, highpaying salaries, and worklife balance.
What you will learn:
 What an Actuary is
 What Actuaries do
 How to become an Actuary
 What the Casualty Actuarial Society is
 Why this is an attractive career
 Your next steps
Who should attend?
 Undergraduate students majoring in actuarial science, math, statistics, business, or other related fields
 Undecided undergraduate students with an interest in math, statistics, business, or other related fields.
Go to: CASstudentcentral.org and register to become a student member. It’s free and provides you access to a wealth of tips, tools and resources.
Past Seminars

Fall 2019
Injectivity of polynomial maps and multistationarity in reaction networks
Professor Casian Pantea, West Virginia University
Friday, Nov 08th  1:00pm – BAIL 201
The capacity of biochemical reaction networks to operate at different steady states is crucial in important biological processes like cell division, differentiation, or apoptosis. In this talk we attack the question “when can a certain reaction network admit two or more positive steady states?”, i.e., when can the network be multistationary? This boils down to a difficult question about solutions of some highdimensional polynomial systems, further complicated by the lack of information on coefficient values. However, it turns out that a lot can be said on multistationarity of reaction networks by studying the injectivity of the corresponding polynomial maps. We will survey some classical and some new results on the topic, and illustrate them using relevant biological examples.
The Strange New Universe of Hyperbolic Geometry
Professor Ellen Gasparovic, Union College
Friday, Nov 1st  1:00pm – BAIL 201
The fifth postulate in Euclid's Elements states that, in a plane, given a line l and a point P not on l, there is exactly one line through P that is parallel to l. Although this is an axiom in Euclidean geometry, what happens when you don't assume that the socalled "parallel postulate" holds? The answer is that beautiful nonEuclidean geometries emerge, such as that of the hyperbolic plane (what mathematician Janos Bolyai referred to as a "strange new universe"). In this talk, we will learn about what it means for lines to be "parallel" or "ultraparallel" in this strange new setting, with an eye toward classifying all distancepreserving transformations using the Klein disk model for the hyperbolic plane.
The Congruent Number Problem
Professor Jeff Hatley, Union College
Thursday, Oct 24th  1:00pm – BAIL 207
The Congruent Number Problem asks the following simplesounding question: which rational numbers occur as the area of a right triangle with sides of rational length? For example, the familiar (3,4,5) right triangle has area 6, so 6 is a congruent number; but Fermat showed in the year 1640 that 1 is not a congruent number. Our investigation of this question will lead to a surprising and beautiful interaction between algebra and geometry, bringing us to the forefront of modern number theory and a math problem with a $1 Million prize.
Joint MathCS Student Seminar
DeepFake the Menace?
Dr. Siwei Lyu
University at Albany
Thursday, Oct 17th  1:00pm – VART 204
The advancements of AI technology, in particular, deep generative models, have enabled the creation of fake images, audios and videos in ways that have not been possible before. Such fake videos, commonly known as the DeepFakes, are eroding our trust to digital media and causing serious ethical, legal, social, and financial consequences. In this talk, I will briefly review the technologies behind the creation of DeepFakes, and then introduce current detection methods of such fake videos and measures that can obstruct the generation of DeepFakes, as well as general technical aspects to combat DeepFakes.
The Interface of Science, Engineering, and Statistics
Professor Roger Hoerl  Union College
Thursday, Oct 10th, 1:00pm, BAIL207
In essence, science expands our understanding of the fundamental workings of the natural world. Engineering, on the other hand, takes our knowledge of the natural world and attempts to apply it in some way that benefits society. Real engineering applications typically venture beyond the boundaries of our scientific knowledge, resulting in uncertainty, and with some degree of "trial and error" required. Google's experiences with selfdriving cars would be an obvious example. At its best, statistics accelerates science and engineering by efficiently filling in the gaps in our scientific theory using empirical data analysis. This seminar will illustrate these concepts using a case study from the author's previous experience as a statistical intern at the DuPont Company.
Connecting STE with M
Professor Robert Rogers  SUNY Fredonia  20192020 "MAA Seaway Section Distinguished Lecturer"
Thursday, Oct 3rd, 1:00pm, VART204
Theoretic chemistry, internet security, kidney stone treatment, airfoil design; what connects these seemingly diverse science, technology, and engineering topics? This talk will explore the mathematics behind these topics. Furthermore, the mathematical topics required to understand these applications only involve drawing, counting, numbers, some geometry, and some imagination.
Thursday, September 26th, 1:00pm, Bailey 207
Featuring: Student talks
Meichai Chen (Class of 2020), Herschel Norwitz (Class 2021), and
Mushan Zhong (Class of 2020)
**************************************
Meichai Chen ('20)
Weak Orders and Utility Functions
A weak order is a complete and transitive order on a set X, whose elements we refer to as preferences. In this talk, we will explore the connections between weak orders and utility functions. We will then briefly discuss how weak orders and utility functions arise in expected utility theory and prospect theory, and conclude with a short description of how these concepts are used in a study regarding stereotype threat.Herschel Norwitz ('21)
Distinguishing between Forced and Natural oscillations on the Power Grid
Oscillations are always occurring on the grid. The two forms of oscillations that occur are natural and forced. Observing natural oscillations can tell the health of the system, unfortunately forced oscillations occur that don't effect the health of the system but can make it appear as though the system is unhealthy. In this research a dynamometer and a DC motor were used to inject a forced oscillations into the outlet. Then using Matlab and a python program measurements are taken from an outlet so see if it is not only possible to observe the oscillations but distinguish them.
Mushan Zhong ('20)
Use of Nonlinear Models in Analyzing Experiments with Both Mixture and Process Variables
When conducting statistics experiments; In most cases we can experiment with different combinations of variables without restrictions. While there are some other cases in which the experimental variables are ingredients, and must sum to 100%. These are called mixture variables. Our research focused on how to approach problems with both process and also mixture variables. We tested different models to see how well they could fit a given set of data, as well as how well they predicted new data. The objective was to develop models that can be applied to smaller data sets, which would allow researchers to run smaller, cheaper, and faster experiments.Featuring: Student summer research
Dan Resnick (class 2021)
Sam Kemp (class 2021)
Friday, September 20th, 1:00pm, Bailey 207
Dan Resnick (class 2021)
Stellar Wind Collisions: Thin Shell Geometry
I will be talking about the theory behind the stellar wind problem and the assumptions/setup to where we started working. I will discuss the methods we used and where we stopped on the problem, and where we plan to go forward with the project.Sam Kemp (class 2021)
Simulation of Forces Between Inclusions on a Lipid Bilayer
A program was written in C++ to simulate the forces between two inclusions on a lipid bilayer using the finite element method. This was first done using Dirichlet boundary conditions and then with mixed boundary conditions at the edge of the inclusions. 
Spring 2019
The Historical Roots of Gödel’s Theorems
Professor Andrea Pedeferri  Philosophy Department @ Union College
Tuesday, May 28th, 1:00pm, Bailey 207
At the beginning of “On formally undecidable propositions of Principia Mathematica and related systems” Gödel writes: “The development of mathematics toward greater precision has led [...] to the formalization of large tracts of it, so that one can prove any theorem using nothing but a few mechanical rules.” In just few sentences Gödel summarizes a century of key developments in mathematics that made that period one of the most exciting and optimistic for the discipline. As Hilbert wrote in 1925 and in 1930 “we are all convinced that [...] in mathematics there is no ignorabimus”, “We must know. We will know”.
Then comes 1931. Gödel writes: “One might therefore conjecture that these axioms and rules of inference are sufficient to decide any mathematical question [...]. It will be shown below that this is not the case [...]. The precise analysis of this curious situation leads to surprising results concerning consistency proofs for formal systems.” The impact of Gödel’s results was immense.
In my talk I will follow the main developments of mathematics highlighted by Gödel in order to show how they are crucial to understand the impact and the reach of Gödel’s theorems and to fully appreciate their dramatic but revolutionary nature.
Rationalizable Voting Rules and the SCorrespondence
Professor Ashley Piggins, Department of Economics, National University of Ireland, Galway (joint work with Conal Duddy, Department of Economics, University College, Cork)
Tuesday, May 21st, 4:00pm, Bailey 207
Perhaps the most important feature in Kenneth Arrow’s famous “Impossibility Theorem” (which helped him earn a Nobel prize in Economics) is IIA – the Independence of Irrelevant Alternatives condition on voting rules, aka social choice. We introduce a related but new social choice property, the Sindependence condition. We characterize the “Scorrespondences” – those social choice rules that satisfy Sindependence along with three more standard axioms: strong Pareto optimality, neutrality and anonymity. This class is closely related to the Srules of Bossert and Suzumura (2008a, J. Econ. Theory 138, 311320). Sindependence can be justified by a new rationalizability argument that shows it is equivalent to assuming IIA in a somewhat different framework.
The History of Fermat's Last Theorem
Professor Ravi Ramakrishna, Cornell University
Thursday, May 16th, 1:00pm, Bailey 207
In 1994, Wiles, assisted by Taylor, finally settled the 340yearold question of Fermat's Last Theorem. In this talk I will give some of the history of this problem, with particular focus on events of 1847 and the 198090s. I'll then talk a little about developments off the last 25 years in the subject.
This talk is NOT aimed at faculty in number theory. It is intended for undergrads that like math, but have not taken many upper level courses.
Mathematical Modeling in Computational Neuroscience
Paulina Volosov, Rensselaer Polytechnic Institute
Thursday, May 2nd, 1:00pm, Bailey 207, with lunch at 12:30pm in Bailey 204
Computational neuroscience is a field of active research for applied mathematicians. The brain has been actively studied since the second half of the 19th century, but there are still an endless number of unanswered questions about how and why the brain works the way it does.
This presentation will give a basic introduction to some of the questions asked in neuroscience and show how a mathematical model can be built and used to shed light on this complicated biological system. Namely, how can a mathematician attempt to learn about the structure of the brain and networks of neurons? What is it that a mathematical model tries to accomplish? And why is this useful?Who Discovered Integral Calculus?
Professor Emeritus Julius Barbanel, Union College
Thursday, April 25th, 1:00pm, Bailey 207, with lunch at 12:30pm in Bailey 204
Isaac Newton and Gottfried Leibniz (both working in the late 17th and early 18th centuries CE) are generally considered to be the inventors of calculus. We will argue in this talk that part of the credit for this discovery should be given to the ancient Greek mathematician Archimedes (who worked in the 3rd century BCE). Archimedes pursued two lines of research involving areas and volumes. These approaches, known as the Method of Exhaustion and the Mechanical Method, can be viewed as early examples of ideas that we think of as being part of integral calculus. We will focus on Archimedes’ Method of Exhaustion.
Presenting Mathematics  an open discussion
Professor Leila Khatami and Professor Jue Wang, Union College
Thursday, April 18th, 1:00pm, Bailey 207, with lunch at 12:30pm in Bailey 204
As Steinmetz symposium approaches, many students are contemplating their presentations and are thinking about ways to make an engaging presentations to effectively share their work with fellow students, family members, and professors. Even those who are not presenting this year, will most probably present their work in the future. In this seminar, we will talk about some of the characteristics of a good mathematics presentation, as well as some of common missteps to avoid. As part of the discussion, we will also watch and analyze a short sample presentation.
Math, ECBE, Physics and Astronomy joint seminar
Thursday April 11, 2019, during common hour in Karp 005
Towards CyberPhysical Electrical Power Systems: where the laws of nature and the rules of algorithms collide!
Luigi Vanfretti
Electrical, Computer, and Systems Engineering, RPIElectrical power networks are undergoing unprecedented changes. On one hand, the adoption of distributed energy resources (DER) and renewable energy sources (RES), both of which have a large degree of variability in small timescales, puts challenges to the traditional, historicalandexperiencebased design and operation of electrical power networks. On the other hand, digitization and automation, opens opportunities for a more carbon neutral electrical energy system by helping to harmonize these new energy sources with the rest of the power grid, not without also bringing along the potential threats of the cyber world. This talk aims to give an overview of these challenges, and to present different research efforts conducted by the presenter to address how to transform today’s electrical grid into a cyberphysical power system. This includes the development of an experimental facility to conduct, realtime hardwareintheloop simulation experiments of power networks with “cyber” assets. This approach allows to characterize how the interaction of systems governed by the laws of nature will interact with engineered systems governed by rules of algorithms. Finally, with the rise of electrification in transport, and in particular aircraft, and the rise of more autonomous machines, the talk will also discuss the need for development of a new course on modeling and simulation for cyberphysical systems (CPS) and the teaching approach adopted which brings a “digital” toolbox and knowhow to the next generation of electrical engineers that will have to increasingly deal with complex CPS.

Winter 2019
The Spectacular Spectral Theory
Ehssan Khanmohammadi, Union College
Thursday, March 7th, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
Do you know the reason for the collapse of the Tacoma Narrows Bridge in 1940? Have you ever wondered about the mathematical idea behind Google’s page ranking and Netflix’s movie recommendation? Do you know why scientists believe that distant stars are largely composed of hydrogen?
This talk is an invitation to the spectacular spectral theory, which is the key to answering all of these questions.Using linear algebra to understand knots
Cynthia Curtis, Professor of Mathematics at The College of New Jersey – Union College Class of 1987
Thursday, February 14th, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
Knots are prevalent in nature, and the study of knotting is important in diverse areas such as DNA, bonding of molecules, and statistical mechanics. Understanding knots has been fundamental within mathematics to our ability to understand threedimensional spaces. In this talk we use linear algebra to generate polynomials, which help decide whether two given knots are different. This is a surprisingly hard question! The polynomials can also help us know when to look for hidden symmetries in the knots. The first knot polynomial we introduce was found by James Waddell Alexander II in 1923. We then discuss new polynomials arising from research with undergraduates Vincent Longo, Alyssa Springstead, and Hoang Cao at The College of New Jersey.
Generalizing composition of functions and Operads
Peter Bonventre, Union College Class of 2011
Friday, February 8th, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
Given two singlevariable functions, we are allowed to take their composite to produce a new function again of a single variable. In this talk, we will ask: “In what other contexts does ‘composition of functions’ make sense?”. We will slowly broaden our definitions of “function” and “composition”, starting with the types of functions that appear in the Calculus sequence, and moving to include wellbehaved geometric figures. This will lead us to the abstract concept of an operad. We will give several examples, as well as an interpretation of what these new objects can do for us.
The Joy of Abstraction
Kimmo Rosenthal, Union College
Thursday, January 31st, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
The imagination is the only genius. It is intrepid and eager and the extreme of its achievement lies in abstraction Wallace Stevens.
It may seem incongruous for the epigraph to a math talk to be from one of the great American poets. However, while the ubiquity and utility of mathematics is widely acknowledged, its burnish of aestheticism is much less so. Can the old dictum “art for art’s sake” be replaced by “math for math’s sake”? In this day and age, when relevance, applicability, and connections with other disciplines are touted as paramount, is there still a place for purely abstract mathematics viewed more as an intellectual art form? Abstraction has always appealed to me and indeed guided me. Why does it often provoke outright hostility? We shall follow the path of abstraction from the set theory of Cantor (called a “corrupter of youth”) to pointset topology, followed by the mysterious emergence of Bourbaki (the mathematician who never existed), and finally category theory, which earned the epithet of “abstract nonsense”. Of course, there will be some mathematics along the way, reasonably modest in scope.
Hall’s Marriage Theorem
Alan Taylor, Union College
Thursday, January 24th, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
Suppose we have a collection of women and a collection of men, and each woman finds some of the men acceptable (and the rest not). When is it possible to match each woman with a man she considers acceptable, subject to the obvious constraint that the matching be one to one? The answer to this metaphorical question is a beautiful result in finite combinatorics known as Hall’s marriage theorem. We will discuss Hall’s theorem, sketch a proof of it, and consider a couple of natural questions it suggests, all with the hope of providing an illustration of how research gets done in mathematics.
Summer Opportunities for Math Students
Thursday, January 17th, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
This week’s seminar will focus on ways in which you can put your mathematical skills to use over the summer.
Julia Greene ’19 will speak about the Teaching Experiences for Undergraduates Program, Professor Jeff Hatley will speak about Research Experiences for Undergraduates, and Keri Willis of the Becker Career Center will speak about summer internships.

Fall 2018
Turning the lights out, mathematician style
Leila Khatami, Union College
Thursday, November 1st, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
“LIGHTS OUT!” is a single player game played on a 5 by 5 grid where each cell has a button that can be turned on or off. Pressing a button toggles the light in the cell and its neighboring cells. The game starts with some cells turned on and some turned off. The goal of the game is to turn all cells off. The game was originally introduced in 1995 as a handheld electronic came. Nowadays, the original game, as well as many of its variants, are readily accessible in app stores and elsewhere. It is not obvious (or even true!) that all starting configurations of the game are “solvable”. In this talk, we use mathematical tools to see if a game is “solvable”. We also briefly discuss ways to find the most efficient solutions for solvable games.
Solving the General Cubic Equation
ax3ax3+bx2bx2+cx+d=0cx+d=0
Paul Friedman, Union College
Thursday, October 25th, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
The solution to the general quadratic equation,
ax2+bx+c=0ax2+bx+c=0,
is wellknown to most high school students:
It was also known to many “ancient” cultures … some dating back to 2000 BC! However, the solution to the general cubic equation, ax3+bx2+cx+d=0ax3+bx2+cx+d=0, is not as well known, and it was not found until the 1500s.In this talk, we will look at how the Renaissance mathematicians Scipione del Ferro, Tartaglia, and Cardano, solved the cubic equation, though we will do so using modern language and notation. As a cute consequence, we will be able to derive some remarkable identities, such as:
Fair Division of a Graph: Envy Freeness up to one Good, or Two
William Zwicker, Union College
Thursday, Oct 18th, 1:00pm, Bailey 207, with reception at 12:30pm in Bailey 204
Countries A and B are dividing up a disputed island with several cities, linked by roads:

 Each city must go entirely to A, or entirely to B
 A city may be worth more to one country than to the other
 You must be able to drive among A’s cities without going through B’s
Can cities be allocated in a way that leaves neither country jealous of the other’s share?
No – not in general. But with certain road networks one can always get within one city of this ideal. Which networks are these? With more than 2 countries, the question gets harder . . . in interesting ways.
In its “classical” setting Fair Division concerns sharing a single, continuously divisible resource. Some solutions can be adapted to this new setting, but a lot needs to change.
Forms of Remigration – Émigré Jewish Mathematicians and Germany in the Immediate PostWar Period
Volker Remmert, , of the Bergische Universitat Wuppertal
Tuesday, Oct 9th, 4:45pm, Bailey 207, with reception at 4:15pm in Bailey 204
Over the last twenty years or so there has been a steady flow of historical studies on remigration into Germany in the immediate postwar period. These studies have described three main forms of academic remigration to Germany after World War II:
1) returning to universities in Germany on a permanent basis as university professors;
2) returning as visiting professors, assessing Germany without any obligation to stay;
3) returning for guest lectures and academic visits.
In this context my interest is in Jewish émigré mathematicians and their stance to Germany in the immediate postwar period.
Math, Music, and Health Science
Danielle Gregg ’19 and Robert Righi ’19, Union College Undergraduates
Thursday, Oct 4th, 1:00pm, Bailey 207
Much recent research has focused on discerning topological and geometric features of data. For example, by observing the “birth” and “death” of holes via an algebraic method known as persistent homology, we can distinguish noise from significant features in data. In analyzing the “shape” of data our research diverges into two separate fields: music and health science. How can one use geometric and topological methods to classify a variety of degenerative diseases of the eye or compare songs within an artist’s discography? Come learn about what two Union students researched over the past summer as well as the often nonlinear research process.
Action Graphs and Catalan Numbers
Julie Bergner, University of Virginia and Cornell University
Thursday, Sept 27th, 1:00pm, Bailey 207
The Catalan numbers are given by a recursivelydefined sequence and arise from over 200 different kinds of combinatorial objects. In 2013, two of my undergraduate research students, Gerardo Alvarez and Ruben Lopez, showed that a family of directed graphs called action graphs gives a new way to obtain this sequence. Since these graphs are defined inductively, one might ask what sequences we can get by using a different initial graph but the same induction process. Last year, three more students, Cedric Harper, Ryan Keller, and Mathilde RosiMarshall, looked into this question. They found new families, called kkinitial action graphs, which produce selfconvolutions of the Catalan sequence. In this talk we’ll introduce the sequences and graphs involved and talk about how these comparisons were made.
Cutting Up Space: Hilbert’s Third Problem and the Dehn Invariant
Jonathan Campbell, Vanderbilt University
Friday, Sept 21st, 1:00pm, Bailey 207
Give two polyhedra of equal volume, can you cut up one into a finite number of pieces, and reassemble it into the other? This was a problem posed by Hilbert in a famous address. I’ll go through the two dimensional analogue of this problem, and present Dehn’s beautiful solution to Hilbert’s question. Time permitting, I’ll give some hint of how this easily stated problem shows up in my own research.
Counting sudokus
Professor Brenda Johnson, Union College
Thursday, Sept 13th, 1:00pm, Bailey 207
Sudoku is a popular puzzle involving a 9×9 grid in which one has to arrange the numbers 1 through 9 so that each row, column, and block contains all nine numbers. There are many interesting mathematical questions involving sudoku puzzles. In this talk, we’ll focus on a couple of questions related to counting sudokus. After discussing how many possible solutions there are for 9×9 and 4×4 sudokus, we’ll look at ways in which one can generate new sudokus from old ones, and whether or not these techniques can be used to generate all sudokus of a given size.
