# Colloquia and Seminars

To join the email distribution list of the cs colloquia, please visit the list subscription page.Computer Science events calendar in HTTP ICS format for of Google calendars, and for Outlook.

Academic Calendar at Technion site.

- Bioinformatics Forum
- BizTEC Forum
- ceClub
- CGGC Weekly Seminar
- Coding Theory Seminar
- Colloquia
- Haifux, Haifa Linux Club
- Pixel Club
- Theory Seminar

## Upcoming Colloquia & Seminars

### CGGC Seminar: Moebius Geometry Processing

- Speaker:
- Amir Vaxman (Utrecht University)
- Date:
- Sunday, 28.5.2017, 13:30
- Place:
- Room 337 Taub Bld.

The mainstream approaches in digital geometry processing utilize triangular (simplicial) meshes, discretize differential quantities using finite-element function spaces, and describe transformations with piecewise affine maps. I will describe how Moebius geometry provides an original alternative to discrete differential geometry, by using circles as its basic elements, and describing quantities like conformality and regularity through the invariant cross-ratio. This theory allows for various applications, such as polygonal (non-triangular) mesh deformation, interpolation, and symmetric realization of unconventional mesh patterns.

### Coding Theory: Codes for Graph Erasures

- Speaker:
- Lev Yohananov (CS, Technion)
- Date:
- Sunday, 28.5.2017, 14:30
- Place:
- Taub 601

Motivated by systems where the information is represented by a graph, such as neural networks, associative memories, and distributed systems, we present in this work a new class of codes, called codes over graphs. Under this paradigm, the information is stored on the edges of an undirected graph, and a code over graphs is a set of graphs. A node failure is the event where all edges in the neighborhood of the failed node have been erased. We say that a code over graphs can tolerate ρ node failures if it can correct the erased edges of any ρ failed nodes in the graph. While the construction of such codes can be easily accomplished by MDS codes, their field size has to be at least O(n^2), when n is the number of nodes in the graph. In this work we present several constructions of codes over graphs with smaller field size. In particular, we present optimal codes over graphs correcting two node failures over the binary field, when the number of nodes in the graph is a prime number. We also present a construction of codes over graphs correcting ρ node failures for all ρ over a field of size at least (n+1)/2−1, and show how to improve this construction for optimal codes when ρ=2,3.

### CGGC Seminar: Obstacle-Ginzburg-Landau Functionals

- Speaker:
- Orestis Vantzos (CS, Technion)
- Date:
- Monday, 29.5.2017, 13:30
- Place:
- Room 337 Taub Bld.

This work proposes an algorithm for computing dense packings of congruent circles inside general 2D containers. Unlike the previous approaches which accept as containers, only simple, symmetric shapes such as circles, rectangles and triangles, our method works for any container with a general, freeform (spline) boundary.

In contrast to most previous approaches which cast the problem into a non-convex optimization problem, our method attempts to maximize the number of packed circles via a perturbation approach and consists of two main phases.

We will discuss a variation of the Ginzburg-Landau functional, a common tool in applications such as image segmentation (Ambrosio-Tortorelli) and phase-field methods in fluid simulation, involving a so-called "double-obstacle" barrier term (first studied by Elliott and Blowey).

We will describe fast (GPU-optimized) variational solvers for gradient flows of these functionals (Allen-Cahn and Cahn-Hilliard equivalents), and also look into certain higher-dimensional generalisations.### TCE Workshop: 2017 Stephen and Sharon Seiden Frontiers in Engineering and Science

- Date:
- Monday, 5.6.2017, 09:30
- Place:
- TCE, TECHNION

You are invited to the upcoming 2017 Stephen and Sharon Seiden Frontiers in Engineering and Science Workshop. This year, the workshop will be titled "Beyond CMOS: From Devices to Systems" and will be held at the Technion, Haifa, Israel on Monday-Tuesday, June 5-6, 2017.

This workshop will bring together researchers and leaders from academia and industry to discuss the many different aspects of emerging solid state memories including device physics, circuits, architecture, reliability, security, and systems. These technologies include RRAM, PCM, 3D Xpoint, STT MRAM, CBRAM, memristors, and many others from all of these fields, including executives from industry who will discuss the commercialization aspects of these technologies.

A call for posters will follow soon, as well as the final program. Registration opens on March 15th, 2017.

More details will be available on the workshop website.

### CGGC Seminar: Design of 3D printed mathematical art

- Speaker:
- Henry Segerman (Oklahoma State University)
- Date:
- Monday, 5.6.2017, 13:30
- Place:
- Room 337 Taub Bld.

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. Within the parametric setting, there are still better and worse ways to proceed. For example, a geometric representation should demonstrate as many of the symmetries of the object as possible. There are similar issues in making three-dimensional representations of higher dimensional objects. 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).### How to Find Cryptographic Needles In Exponentially Large Haystacks

- Speaker:
- Adi Shamir - COLLOQUIUM LECTURE
- Date:
- Tuesday, 6.6.2017, 14:30
- Place:
- Room 337 Taub Bld.
- Affiliation:
- Weizmann Institute
- Host:
- Yuval Filmus

One of the most common algorithmic tasks is to find a single interesting event (a needle) in an exponentially large collection (haystack) of N=3D2^n possible events, or to demonstrate that no such event is likely to exist. In particular, we are interested in the problem of finding needles which are defined as events that happen with an unusually high probability of p>>1/N in a haystack which is an almost uniform distribution on N possible events. Such a search algorithm has many applications in cryptography and cryptanalysis, and its best known time/memory tradeoff requires O(1/Mp^2) time given O(M) memory when the search algorithm can only sample values from this distribution.

In this talk I will describe much faster needle searching algorithms when the distribution is defined by applying some deterministic function f to random inputs. Such a distribution can be modelled by a random directed graph with N vertices in which almost all the vertices have O(1) predecessors while the vertex we are looking for has an unusually large number of O(pN) predecessors. When we are given only a constant amount of memory, we propose a new search methodology which we call NestedRho. As p increases, such random graphs undergo several subtle phase transitions, and thus the log-log dependence of the time complexity T on p becomes a piecewise linear curve which bends four times. Our new algorithm is faster than the O(1/p^2) time complexity of the best previous algorithm in the full range of 1/N < p < 1, and in particular it improves it for some values of p by a significant factor of sqrt {N}. When we are given more memory, we show how to combine the NestedRho technique with the parallel collision search technique in order to further reduce its time complexity. Finally, we show how to apply our new search technique to more complicated distributions with multiple peaks when we want to find all the peaks whose probabilities are higher than p.

The talk will be self contained, requiring no prior knowledge of cryptography. It is joint work with Itai Dinur, Orr Dunkelman, and Nathan Keller.

Short Bio (from Wikipedia):

Shamir received a BSc degree in mathematics from Tel Aviv University in 1973 and obtained his MSc and PhD degrees in Computer Science from the Weizmann Institute in 1975 and 1977 respectively. After a year postdoc at University of Warwick, he did research at MIT from 1977-1980 before returning to be a member of the faculty of Mathematics and Computer Science at the Weizmann Institute. Starting from 2006, he is also an invited professor at Ecole Normale Superieure in Paris.

He is a co-inventor of the RSA algorithm (along with Ron Rivest and Len Adleman), a co-inventor of the Feige-Fiat-Shamir identification scheme (along with Uriel Feige and Amos Fiat), one of the inventors of differential cryptanalysis (along with Eli Biham), and has made many contributions to the fields of cryptography and computer science. Shamir's other numerous inventions and contributions to cryptography include the Shamir secret sharing scheme, the breaking of the Merkle-Hellman knapsack cryptosystem, visual cryptography, and the TWIRL and TWINKLE factoring devices. Shamir has also made contributions to computer science outside of cryptography, such as finding the first linear time algorithm for 2-satisfiability and showing the equivalence of the complexity classes PSPACE and IP.

Shamir has received a number of awards, including the 2002 ACM Turing Award, the Paris Kanellakis Theory and Practice Award, the Erdoes Prize, the 1986 IEEE W.R.G. Baker Award, the UAP Scientific Prize, the Vatican's PIUS XI Gold Medal, the 2000 IEEE Koji Kobayashi Computers and Communications Award, the 2008 Israel Prize, and the 2017 Japan Prize.### CGGC Seminar: Precise Algebraic-based Swept Volumes for Arbitrary Free-form Shaped Tools towards Multi-axis CNC Machining Verification

- Speaker:
- Jinesh Machchhar (CS, Technion)
- Date:
- Sunday, 11.6.2017, 13:30
- Place:
- Room 337 Taub Bld.

We will discuss a variation of the Ginzburg-Landau functional, a common tool in applications such as image segmentation (Ambrosio-Tortorelli) and phase-field methods in fluid simulation, involving a so-called "double-obstacle" barrier term (first studied by Elliott and Blowey).

We will describe fast (GPU-optimized) variational solvers for gradient flows of these functionals (Allen-Cahn and Cahn-Hilliard equivalents), and also look into certain higher-dimensional generalisations.### CRYPTODAY 2017

- Date:
- Thursday, 15.6.2017, 09:00
- Place:
- CS Taub Auditorium 1

The 2017 Workshop in Cryptology will be held on Thursday, June 15 2017, between 9:00-17:15, in Auditorium 1, at the CS Taub Building, Technion.

Most talks will be held in Hebrew and Keynote speaker will be Dr. Marc Stevens who will talk about his recent work that found a collision of SHA-1. Other highlights will be talks about virtual coins and blockchains, and other topics.

More details and program, including lecture abstracts, (free but required) registration and arrival directions.

You are all invited!### Effective deductive verification of safety of distributed protocols in unbounded systems

- Speaker:
- Mooly Sagiv - COLLOQUIUM LECTURE
- Date:
- Tuesday, 20.6.2017, 14:30
- Place:
- Room 337 Taub Bld.
- Affiliation:
- Tel-Aviv University, School of Computer Science
- Host:
- Yuval Filmus

T B A

### The 7th Annual International TCE Conference on Coding for Storage and Information Systems

- Date:
- Wednesday, 21.6.2017, 08:30
- Place:
- CS Taub Building

The 7th annual international TCE conference will take place on Wednesday-Thursday, June 21-22, 2017 at the Technion CS Taub Building and will focus onadvancing information technologies like distributed storage and cloud systems, new and emerging memory technologies, biological systems and genomics, secrecy and security, reliable computation and big data, communications and networking.

Conference Chairs: Eitan Yaakobi (CS Technion) and Yuval Cassuto (EE Technion)

Tentative list includes:

· Alexander Barg, University of Maryland, USA

· André Brinkmann, Universität Mainz, Germany

· Johannes Gutenberg, Universität Mainz, Germany

· Lara Dolecek, UCLA, USA

· Ryan Gabrys, University of Illinois at Urbana-Champaign, USA

· Warren Gross, McGill University, Canada

· Danny Harnik, IBM, Israel

· Michael Kazhdan, Johns Hopkins University, USA

· Idit Keidar, Technion, Israel

· HanMao Kiah, NTU, Singapore

· P. Vijay Kumar, Indian Institute of Science, Bangalore, India

· Olgica Milenkovic, University of Illinois at Urbana-Champaign, USA

· Paul H. Siegel, UC San Diego, USA

· Eran Sharon, SanDisk/WD, Israel

· Emina Soljanin, Rutgers University, USA

· Ido Tal, Technion, Israel

· Alexander Vardy, UC San Diego, USA

· Zohar Yakhini, IDC, Israel

Registration and more details about the conference program and information on TCE.