The CUNY Data Science and Applied Topology Reading Group is joint between the Mathematics and Computer Science programmes. We meet Fridays 11.45 -- 12.45 in GC 3309. You can contact us at cunygc@appliedtopology.nyc.

Our plan is to primarily read and discuss seminal papers in data science, in applied topology and in topological data analysis. Each seminar one participant takes the responsibility to present a paper and prepare items for discussion. We expect occasionally to be able to invite external speakers.

## Schedule

Current schedule can be found here.

We will be sending out announcements through a mailing list; you can subscribe here.

## Organizers

- Mikael Vejdemo-Johansson, Computer Science Programme, CUNY Graduate Center; Department of Mathematics, CUNY College of Staten Island
- Azita Mayeli, Mathematics Programme, CUNY Graduate Center; Department of Mathematics, CUNY Queensborough Community College
- Chao Chen, Computer Science Programme, CUNY Graduate Center; Department of Computer Science, CUNY Queens College

## Suggested papers

We have compiled a list of papers that might be interesting to present.

# Schedule

### Inaugural meeting

For an inaugural meeting we will discuss paper assignments and focus interests for our active seminar participants. There will be pizza and brownies.

### Topology and Data

TBD

### The Forman gradient: a discrete tool for topology-based data analysis

Morse theory studies the relationships between the topology of a shape and the critical points of a real-valued smooth function defined on it. It has been recognized as an important tool for shape analysis and understanding in several applications, including physics, chemistry, medicine, and geography. Morse theory is defined for smooth functions, but recently a discrete counterpart, called Discrete Morse Theory (DMT), has been proposed in an entirely combinatorial setting. DMT introduces the idea of discrete Morse functions as functions that assign values to all the cells of a complex. Based on a discrete Morse function we can impose a partial pairing on such cells and eventually build a combinatorial gradient, also called Forman gradient. The Forman gradient is a very powerful tool as it provides a compact way to represent data without altering its homology. This talk will cover our contribution in developing computational tools, based on the Forman gradient, for the analysis of 2D and 3D scalar fields. I will describe in detail our compact representation for the Forman gradient defined on simplicial complexes and how it can be adapted to the n-dimensional case. Moreover, I will describe our recent work on multivariate data (i.e., collections of scalar fields), and how we can adapt the Forman gradient for analyzing such data in a computationally efficient way.

### Extracting Insights from Complex Shapes using Topology

TBD

### Persistent Cohomology and human motion

TBD: Discuss persistent cohomology, circular coordinates and applications to motion capture.

### Cancelled

Cancelled

### Single cell mapper analysis

Next-generation high-throughput sequencing has generated an explosion of available genomic data. That holds a great potential for exploring biological systems with unprecedented resolution at the single-cell level. However, single-cell sequencing yields complex data output and implies technical challenges to traditional computational methods, which are mostly based on clustering and combinatorics. In this talk we will give a general perspective on the challenges and advances in the field of single-cell and associated data analysis problems. We put special emphasis on topological techniques.

### Barcodes: The Persistent Topology of Data

TBD

### The fiber of the persistence map

The persistence map is the map that sends a function on a topological space to it's collection of persistence diagrams, which are canonical invariants of filtering a space by sublevel sets and taking homology in each degree. Geometrically, a persistence diagram is simply a configuration of points in the plane. In this talk I will study which configurations of points are possible and what the ramification of this map is for the simplest possible case---functions on the interval. Ongoing work and open problems will also be discussed.

### The Fuglede conjecture holds in the finite vector space \(\mathbb{Z}_p^2\)

We will see that the Fuglede Conjecture holds in $\mathbb{Z}_p^2$, proved by Iosevich/Mayeli/Pakianathan. That is the subsets E of the finite vector space $\mathbb{Z}_p^2$ tiles the space if and only if every function from E to the complex numbers is a linear combination of orthogonal exponential functions. Key ideas of the proof use Fourier transforms of functions from this space, direction sets, and some Galois theory.