A reminder about a fairly new major prize that is highly relevant to the TCS community (won last year by Prasad Raghavendra and David Steurer):

The National Academy of Sciences has initiated the Michael and Sheila Held Prize. The prize of $100,000 will be presented annually. The Prize honors outstanding, innovative, creative and influential research in the areas of combinatorial and discrete optimization, or related parts of computer science, such as the design and analysis of algorithms and complexity theory. The prize is intended to recognize recent work(defined as published within the last eight years). The prize was established in 2017 by the bequest of Michael and Sheila Held.

Nominations are due on October 1, 2018, and information about the submission process can be found at http://www.nasonline.org/held.

PS: You can find information about many other awards related to TCS at the CATCS awards list.

At the recommendation of Craig Gentry, I recently read the book “Factor Man” by Matt Ginsberg. This book is about a computer scientist that discovers an efficient algorithm for SAT, which starts off a international game of intrigue involving the FBI, NSA, Chinese spies, Swiss banks, and even some characters we know such as Steven Rudich and Scott Aaronson.

(However there is no mention of Scott’s role as the criminal mastermind behind the great Philadelphia Airport Heist.)

While it’s by no means “great literature”, Factor Man is a fun page-turner. I think it can be a particularly enjoyable read for computer scientists, as it might prompt you to come up with your own scenarios as to how things would play out if someone discovers such an algorithm. Unsurprisingly, the book is not technically perfect. The technical error that annoyed me the most was that the protagonist demonstrates his algorithm by factoring integers of sizes that can in fact be fairly easily factored today (the book refers to factoring 128 or 256 bit numbers as impressive, while 768 bit integers of general form have been factored, see also this page and this paper). If you just imagine that when the book says “ bit” numbers it actually means *byte* numbers then this is fine. Network security researchers might also take issue with other points in the book (such as the ability of the protagonist to use gmail and blogspot without being identified by neither the NSA nor Google, as well as using a SAT algorithm to provide a “final security patch” for a product).

Regardless of these technical issues, I recommend reading this book if you’re the type of person that enjoys both computer science and spy thrillers, and I do plan to mention it to students taking my introduction to theoretical CS course.

A reflection piece from Scarlett Sozzani, a member of the community. We will be happy to publish additional posts (anonymously or otherwise) on the subject.

By Scarlett Sozzani

In response to and in support of recent activism around sexual assault and inclusivity at large, I want to take an opportunity to argue that issues of harassment, discrimination, bullying, and other egregiously insupportable actions can only exist when the victims are perceived to be weak, vulnerable, and powerless. And this kind of perception is often (and unwittingly) perpetuated through microagressions by many members of our academic community. Even though microaggressions are arguably even more frequent than outright forms of discrimination and harassment, this issue remains largely unaddressed.

Microaggression is formally defined (on dictionary.com) as:

*a statement, action, or incident regarded as an instance of indirect, subtle, or unintentional discrimination against members of a marginalized group such as a racial or ethnic minority.*

A microaggression is difficult to identify because it is so subtle – what one person may consider a microaggression may seem like merely a rude or tactless comment to another person. And comments that do not overtly mention race, gender, class, sexual orientation, etc. are more difficult to directly attribute as an act of microaggression. Furthermore, microaggressions are sometimes unintentional, so the perpetrator might not even realize they are committing a microaggression against someone. It’s a very personal judgment, so perhaps a good question to ask is: “What is the likelihood that the perpetrator would have made this same comment to a person who identifies with the privileged majority?”

Microagressions also come in many forms: not just in words, but also in tone, attitude, gestures, writing, and in all forms of interaction. The accumulated damage over many instances, over time, cannot be understated. It elicits an intuitive response in the receivers of such microaggressions – a nagging feeling of self-doubt that one doesn’t belong, or isn’t good enough, or isn’t as good as the rest of the people in the room.

And beyond the predominantly discriminative definition of a microaggression, I would argue that any action that makes a person feel like their contributions are not valuable, and that they are not good enough to be standing where they are, is counterproductive to the collective aspirations of a community, especially an ambitious, high-flying research community.

Here are some examples of a few microagressions that I have felt in my very short time as a graduate student and in my various roles as a colleague, advisee, collaborator, and teaching assistant.

-“It’s a hard paper to read, especially if you don’t have the necessary background.”

-“You should be able to get the fellowship, right? You’re a young girl.”

-“How is that not what I just said?”

-“I erased your Piazza post answering a student’s ask for supplementary materials because I didn’t like the paper you referenced.”

-And the classic: “Hey guys…”

Let’s all aim to do a little bit better. Perhaps even go above and beyond in pushing against the current by acknowledging, highlighting, and talking about hard-earned and worthy contributions from our under-represented mentees and colleagues.

**Authors: **Theo McKenzie, Hermish Mehta, Luca Trevisan **Download:** PDF**Abstract: **In this paper, we study a semi-random version of the planted independent set
problem in a model initially proposed by Feige and Kilian, which has a large
proportion of adversarial edges. We give a new deterministic algorithm that
finds a list of independent sets, one of which, with high probability, is the
planted one, provided that the planted set has size $k=\Omega(n^{2/3})$.

**Authors: **Henok Ghebrechristos, Drew Miller **Download:** PDF**Abstract: **Existing models of computation, such as a Turing machine (hereafter, TM), do
not consider the agent involved in interpreting the outcome of the computation.
We argue that a TM, or any other computation model, has no significance if its
output is not interpreted by some agent. Furthermore, we argue that including
the interpreter in the model definition sheds light on some of the difficult
problems faced in computation and mathematics. We provide an analytic process
framework to address this limitation. The framework can be overlaid on existing
concepts of computation to address many practical and philosophical concerns
such as the P vs NP problem. In addition, we provide constructive proof for the
P vs NP problem under the assumption that the class NP comprises of problems
solvable by non-deterministic algorithms. We utilize the observation that
deterministic computational procedures lack fundamental capacity to fully
simulate their non-deterministic variant.

**Authors: **Ahmad B. Hassanat **Download:** PDF**Abstract: **Finding the diameter of a dataset in multidimensional Euclidean space is a
well-established problem, with well-known algorithms. However, most of the
algorithms found in the literature do not scale well with large values of data
dimension, so the time complexity grows exponentially in most cases, which
makes these algorithms impractical. Therefore, we implemented 4 simple greedy
algorithms to be used for approximating the diameter of a multidimensional
dataset; these are based on minimum/maximum l2 norms, hill climbing search,
Tabu search and Beam search approaches, respectively. The time complexity of
the implemented algorithms is near-linear, as they scale near-linearly with
data size and its dimensions. The results of the experiments (conducted on
different machine learning data sets) prove the efficiency of the implemented
algorithms and can therefore be recommended for finding the diameter to be used
by different machine learning applications when needed.

**Authors: **Laurent Bulteau, Konrad K. Dabrowski, Guillaume Fertin, Matthew Johnson, Daniel Paulusma, Stephane Vialette **Download:** PDF**Abstract: **A partition $(V_1,\ldots,V_k)$ of the vertex set of a graph $G$ with a (not
necessarily proper) colouring $c$ is colourful if no two vertices in any $V_i$
have the same colour and every set $V_i$ induces a connected graph. The
COLOURFUL PARTITION problem is to decide whether a coloured graph $(G,c)$ has a
colourful partition of size at most $k$. This problem is closely related to the
COLOURFUL COMPONENTS problem, which is to decide whether a graph can be
modified into a graph whose connected components form a colourful partition by
deleting at most $p$ edges. Nevertheless we show that COLOURFUL PARTITION and
COLOURFUL COMPONENTS may have different complexities for restricted instances.
We tighten known NP-hardness results for both problems and in addition we prove
new hardness and tractability results for COLOURFUL PARTITION. Using these
results we complete our paper with a thorough parameterized study of COLOURFUL
PARTITION.

**Authors: **Amir Carmel, Dekel Tsur, Michal Ziv-Ukelson **Download:** PDF**Abstract: **The problem of aligning two strings A,B in order to determine their
similarity is fundamental in the field of pattern matching. An important
concept in this domain is the "all scores matrix" that encodes the local
alignment comparison of two strings. Namely, let K denote the all scores matrix
containing the alignment score of every substring of B with A, and let J denote
the all scores matrix containing the alignment score of every suffix of B with
every prefix of A.

In this paper we consider the problem of maintaining an all scores matrix where the scoring function is the LCS score, while supporting single character prepend and append operations to A and N. Our algorithms exploit the sparsity parameters L=LCS(A,B) and Delta = |B|-L. For the matrix K we propose an algorithm that supports incremental operations to both ends of A in O(Delta) time. Whilst for the matrix J we propose an algorithm that supports a single type of incremental operation, either a prepend operation to A or an append operation to B, in O(L) time. This structure can also be extended to support both operations simultaneously in O(L log log L) time.

**Authors: **Itai Ashlagi, Maximilien Burq, Chinmoy Dutta, Patrick Jaillet, Amin Saberi, Chris Sholley **Download:** PDF**Abstract: **We study the problem of matching agents who arrive at a marketplace over time
and leave after d time periods. Agents can only be matched while they are
present in the marketplace. Each pair of agents can yield a different match
value, and the planner's goal is to maximize the total value over a finite time
horizon. First we study the case in which vertices arrive in an adversarial
order. We provide a randomized 0.25-competitive algorithm building on a result
by Feldman et al. (2009) and Lehman et al. (2006). We extend the model to the
case in which departure times are drawn independently from a distribution with
non-decreasing hazard rate, for which we establish a 1/8-competitive algorithm.

When the arrival order is chosen uniformly at random, we show that a batching algorithm, which computes a maximum-weighted matching every (d+1) periods, is 0.279-competitive.

**Authors: **Robert Ganian, Sebastian Ordyniak **Download:** PDF**Abstract: **This paper revisits the classical Edge Disjoint Paths (EDP) problem, where
one is given an undirected graph $G$ and a set of terminal pairs $P$ and asks
whether $G$ contains a set of pairwise edge-disjoint paths connecting every
terminal pair in $P$. Our aim is to identify structural properties (parameters)
of graphs which allow the efficient solution of EDP without restricting the
placement of terminals in $P$ in any way. In this setting, EDP is known to
remain NP-hard even on extremely restricted graph classes, such as graphs with
a vertex cover of size $3$.

We present three results which use edge-separator based parameters to chart new islands of tractability in the complexity landscape of EDP. Our first and main result utilizes the fairly recent structural parameter treecut width (a parameter with fundamental ties to graph immersions and graph cuts): we obtain a polynomial-time algorithm for EDP on every graph class of bounded treecut width. Our second result shows that EDP parameterized by treecut width is unlikely to be fixed-parameter tractable. Our final, third result is a polynomial kernel for EDP parameterized by the size of a minimum feedback edge set in the graph.

**Authors: **Kamil Khadiev, Dmitry Kravchenko **Download:** PDF**Abstract: **We study algorithms for solving Subtraction games, which sometimes are
referred to as one-heap Nim games. We describe a quantum algorithm which is
applicable to any game on DAG, and show that its query compexity for solving an
arbitrary Subtraction game of $n$ stones is $O(n^{3/2}\log n)$. The best known
deterministic algorithms for solving such games are based on the dynamic
programming approach. We show that this approach is asymptotically optimal and
that classical query complexity for solving a Subtraction game is generally
$\Theta(n^2)$. This paper perhaps is the first explicit "quantum" contribution
to algorithmic game theory.

**Authors: **Ran Ben Basat, Xiaoqi Chen, Gil Einziger, Ori Rottenstreich **Download:** PDF**Abstract: **Programmable network switches promise flexibility and high throughput,
enabling applications such as load balancing and traffic engineering. Network
measurement is a fundamental building block for such applications, including
tasks such as the identification of heavy hitters (largest flows) or the
detection of traffic changes.

However, high-throughput packet processing architectures place certain limitations on the programming model, such as restricted branching, limited capability for memory access, and a limited number of processing stages. These limitations restrict the types of measurement algorithms that can run on programmable switches. In this paper, we focus on the RMT programmable high-throughput switch architecture, and carefully examine its constraints on designing measurement algorithms. We demonstrate our findings while solving the heavy hitter problem.

We introduce PRECISION, an algorithm that uses \emph{Probabilistic Recirculation} to find top flows on a programmable switch. By recirculating a small fraction of packets, PRECISION simplifies the access to stateful memory to conform with RMT limitations and achieves higher accuracy than previous heavy hitter detection algorithms that avoid recirculation. We also analyze the effect of each architectural constraint on the measurement accuracy and provide insights for measurement algorithm designers.

**Authors: **Ranveer Singh, Naomi Shaked-Monderer, Avi Berman **Download:** PDF**Abstract: **A block graph is a graph in which every block is a complete graph. Let $G$ be
a block graph and let $A(G)$ be its (0,1)-adjacency matrix. Graph $G$ is called
nonsingular (singular) if $A(G)$ is nonsingular (singular). Characterizing
nonsingular block graphs is an interesting open problem proposed by Bapat and
Roy in 2013. In this article, we give a linear time algorithm to check whether
a given block graph is singular or not.

**Authors: **Janardan Misra **Download:** PDF**Abstract: **Observations are an essential component of the simulation based studies on
artificial-evolutionary systems (AES) by which entities are identified and
their behavior is observed to uncover higher-level "emergent" phenomena.
Because of the heterogeneity of AES models and implicit nature of observations,
precise characterization of the observation process, independent of the
underlying micro-level reaction semantics of the model, is a difficult problem.
Building upon the multiset based algebraic framework to characterize
state-space trajectory of AES model simulations, we estimate bounds on
computational resource requirements of the process of automatically discovering
life-like evolutionary behavior in AES models during simulations. For
illustration, we consider the case of Langton's Cellular Automata model and
characterize the worst case computational complexity bounds for identifying
entity and population level reproduction.

**Authors: **Jake Wellens **Download:** PDF**Abstract: **In this note, we slightly improve the guarantees obtained by Guo and Jerrum
for sampling from the hard disks model in the plane via partial rejection
sampling. Our proof makes use of the fact that if one spreads apart a
collection of disks in the plane, the area of the union of the disks cannot
decrease.

**Authors: **Barbara Geissmann **Download:** PDF**Abstract: **We study the problem of computing a longest increasing subsequence in a
sequence $S$ of $n$ distinct elements in the presence of persistent comparison
errors. In this model, every comparison between two elements can return the
wrong result with some fixed (small) probability $ p $, and comparisons cannot
be repeated. Computing the longest increasing subsequence exactly is impossible
in this model, therefore, the objective is to identify a subsequence that (i)
is indeed increasing and (ii) has a length that approximates the length of the
longest increasing subsequence.

We present asymptotically tight upper and lower bounds on both the approximation factor and the running time. In particular, we present an algorithm that computes an $O(\log n)$-approximation in time $O(n\log n)$, with high probability. This approximation relies on the fact that that we can approximately sort $n$ elements in $O(n\log n)$ time such that the maximum dislocation of an element is at most $O(\log n)$. For the lower bounds, we prove that (i) there is a set of sequences, such that on a sequence picked randomly from this set every algorithm must return an $\Omega(\log n)$-approximation with high probability, and (ii) any $O(\log n)$-approximation algorithm for longest increasing subsequence requires $\Omega(n \log n)$ comparisons, even in the absence of errors.

I just came back from Rio from a great congress. Many great talks and many exciting meetings with old and new friends. I had planned to live-blog on the last four days of the congress but on Monday evening I … Continue reading

I just came back from Rio from a great congress. Many great talks and many exciting meetings with old and new friends. I had planned to live-blog on the last four days of the congress but on Monday evening I realized that this was an unrealistic task and decided instead to blog only on a single day – Monday. A little later I realized this was also unrealistic and decided to limit my blogging to a single great lecture by Peter Kronheimer and Tomasz Mrowka on Knots, three-manifolds and instantons. But in the end I did not live-blog at all. Let me mention that in the talk by Kronheimer and Mrowka (as in others) a two-speaker talk worked beautifully. It could be a good similar idea to even share a single Fields medal between two (or more) coauthors.

Here are the slides for my lecture Noise Stability, Noise Sensitivity and the Quantum Computer Puzzle.

There were many national receptions at the ICM (I missed a few but made it to the Abel reception and Japan’s reception). This led to the idea of having a reception by a mathematical discipline. We are thinking of a combinatorial event in ICM2022 as follows:

**Time:** Tuesday evening – the second week of ICM 2022

**Location:** A park in Saint Petersburg (TBA)

**Activity** (tentative): Light food and drinks will be available (to buy). **Music with a DJ and dancing.**

**Invitees** (tentative): The event will be open for all interested ICM2022 participants.

**T-shirts** (very tentative, other suggestions welcome)

background colors: red, blue, white and rainbow

ICM 2018 could be considered as an excellent conference in combinatorics on its own. There were eleven top-of-the-line speakers (one joint with probability) in wide areas of combinatorics who gave very good talks; a separate session of much combinatorial content on theoretical computer science; many lectures in other sessions (alas, a few conflicting) with interest to combinatorialists; and, in addition, many of the plenary talks had a strong combinatorial content or connections. Like for ICM2010 (Post 1 Post 2) I do plan to write more impressions from ICM2018 at a later time. Meanwhile, a few pictures (more, later).

Amazon has a program for research awards. Check out the process. The focus areas include online advertising for the first time and this should be interesting to researchers in mechanism design, optimization, game theory and multiagent systems, among other things. There is also a lot of interest in machine learning methods in general, and theory in the context of these focus areas. The deadline is Sept 15, 2018. Looking forward to submissions.

Continuing the tradition from 2015, 2016, and 2017, there will be an article in the upcoming edition of the SIGecom Exchanges profiling junior job market candidates (both for postdoc and faculty positions) of the SIGecom community for 2018-2019. These profiles will include the thesis title, research summary, brief biography, and citations to three representative papers. At least one of these papers should have appeared in the ACM Conference on Economics and Computation (EC) or a comparable venue.

To be considered, **submissions must be initiated no later than August 26 and finalized by August 30**. Further instructions for submissions can be found on the submission form. The article will be co-edited by Vasilis Gkatzelis and myself.