MIM UW – great place to work!

Interview with Lucas Pastor, former Postdoc at MIM UW, Warsaw, Poland


Renata Czarniecka: - What made you choose the Institute of Informatics at University of Warsaw (MIM UW ) for your postdoc?

Lukas Pastor: - I found out about MIM UW from my friend, who is a researcher in my field. She told me that prof. Marcin Pilipczuk and his team from MIM UW are very renowned in the field and very nice people. So I decided to apply for the postdoc position. I sent an email with my postdoc research project and CV and then I was asked for a Skype interview. After the interview, Marcin told me that I got the position. I found Marcin and his brother Michał Pilipczuk very kind, open-minded people, and of very strong in mathematics in general.

What advice would you give for future postdocs at MIM UW?

- MIM UW is a great environment for a postdoc, with highly skilled and talented researchers. Do not hesitate to ask around who would be interested in working with you. You will find many research mates!

What have you gained from your postdoc?

- I’ve learned a lot of things thanks to my postdoc. Marcin and  the people I worked with during my stay, shared many different things with me that strengthened my knowledge in the area of the Erdős-Hajnal conjecture. The most important were the proof techniques around this conjecture. I was struck by the fact that each of those results are impressive, clever and yet so little is known about this famous problem.

What’s the potential impact of your work?

- It is hard to tell. We tried very hard and got very little advances but we all learned from this work. Furthermore, I had the opportunity to work with a French PhD student, Marc Heinrich, that made a research visit in MIM UW. It was really extraordinary experience. Together we developed a parameterized algorithms for a graph optimization problem.

What is your direct goal right now?

- My direct goal right now is to give high quality lectures, tutorials and practical work to my students and go deep into my research topics.

What are your plans for the future?

- I would like to tackle some well-known, difficult and complex problems in graph theory with different people, including Marcin and the people I’ve worked with at MIM UW! I would like to try to solve some list-coloring problems. List-coloring problems are very hard and each result, even the smallest, needed hard work. Related to this kind of problems, I would also like to try to attack coloring problems in structured graphs, more precisely, graphs not containing long induced paths.

What makes MIM UW a great place to work?

- MIM UW is a great place to work because of high scientific level. Beside this everybody I’ve met here was very humble and happy to work with a young researcher such as myself. I also appreciate the help provided by the administrative staff at MIM UW. All of them were extremely helpful. In particular Ms. Ewa Puchalska who was super kind and supportive. She even helped me with things not directly related to MIM UW administration, such as renting a flat. Great thing of working at MIM UW was that there was no language barrier. Everybody at the faculty speaks fluent English, especially young people.

How did you find Warsaw as a place to live in?

-Warsaw is an interesting city. There is a lot of nice places  to go out for a drink or eat. I was surprised by the good quality to price ratio in most of the restaurants I went to. Public transport in Warsaw is really well-organized so it was easy to travel around Warsaw thanks to the trams, buses and metro lines. Furthermore, Warsaw is a very safe city, even at night. All the things mentioned above make it a great city to live in for a young foreigner.



Lucas Pastor obtained his PhD in Grenoble under the supervision of Frédéric Maffray and Sylvain Gravier. His research interests focus mostly on graph theory, more precisely structural graph theory and optimization problems in graphs.


During the period from December 2017 to August 2018 he attended a one-year fellowship (postdoc position) at the Institute of Informatics, University of Warsaw, Poland. The position was supported by the ERC Starting Grant CUTACOMBS: “Cuts and decompositions: algorithms and combinatorial properties” led by prof. Marcin Pilipczuk.

homepage: https://fc.isima.fr/~lupasto/

HALG 2019 in Copenhagen on June 14-16, 2019

I was recently asked to chair the 4th Highlights of Algorithms conference (HALG 2019). HALG 2019 will be held in Copenhagen on June 14-16, 2019. First, I wish to see many of you there. HALG works very well and for me it was one of the best algorithmic conferences I attended in recent years. You can read more in a report in EATCS  bulletin. Second, I hope we will have a great program thanks to the help of the following people in the PC:

Susanne Albers (Technical University of Munich)
Edith Cohen  (Google & Tel Aviv University)
Shiri Chechik (Tel Aviv University)
Fabian Kuhn (University of Freiburg)
Seffi Naor (Technion)
Marcin Pilipczuk (University of Warsaw)
Piotr Sankowski (chair - University of Warsaw)
David Shmoys (Cornell University)
Ola Svennson (EPFL)
Mikkel Thorup (University of Copenhagen)
Gregory Valiant (Stanford University)
Ryan Williams (MIT)

The first batch of invitations will be out soon together with the call for nominations, so do not be surprised if you get one.

2018 NCN prizes awarded!

On October 10, 2018, the National Science Centre Awards were presented for the sixth time. The prize, established in 2013 by the NCN Council, is awarded to scientists up to the age of 40 for significant achievements in the field of basic research conducted in Polish scientific institutions. Every year, the prize is given to representatives of three research areas: art, humanities and social sciences, life sciences, natural and technical sciences.

The NCN Award is also a platform for cooperation between business and science. Every year, companies involved in social and research activities are invited to cooperate in funding the awards. Such a formula enables direct support for the young leaders shaping the future of Polish science. This year's NCN Awards have been funded by: Adamed Group, Jastrzębska Spółka Węglowa and the KGHM Polska Miedź Foundation.


We are pleased to announce that this year winner in the group of natural and technical sciences is dr hab. Piotr Sankowski from University of Warsaw, Faculty of Mathematics, Informatics and Mechanics.



Postdoc positions in Warsaw (algorithms)

We announce one-year postdoc positions (with possible extensions) at the Institute of Informatics, University of Warsaw, Poland. The positions are supported by the ERC Starting Grant CUTACOMBS: “Cuts and decompositions: algorithms and combinatorial properties” led by Marcin Pilipczuk and by the ERC Consolidator Grant TUgbOAT: “Towards Unification of Algorithmic Tools” led by Piotr Sankowski.

The CUTACOMBS’ focus is on structural graph theory and parameterized complexity. Example topics include:
* structure of separations in directed graphs, with applications to parameterized algorithms;
* approximability of the disjoint paths problem in various settings;
* structure of hereditary graph classes, such as graph excluding a fixed graph as induced subgraph, with algorithmic and graph-theoretical applications.
More information about the project can be found at http://cutacombs.mimuw.edu.pl/.

The TUgbOAT’s focus is to work on algorithms for core algorithmic problems.
Example topics include:
* faster algorithms for matchings and maximum flow problems;
* optimal online algorithms (when comparing to online opt);
* analyzing structure of real world networks and exploiting it algorithmically.

The theoretical computer science group in Warsaw is strong and growing. Apart from the algorithms group specializing in parameterized and approximation algorithms (Marek Cygan, Łukasz Kowalik, Marcin Mucha, Marcin Pilipczuk, Michał Pilipczuk, Piotr Sankowski), we have also a leading research group in logic and automata (Mikołaj Bojańczyk, Bartosz Klin, Sławomir Lasota).

We are looking for outstanding candidates with a Ph.D. (or soon to obtain a Ph.D.) in Computer Science or Mathematics who have already proven their high scientific potential in the area of algorithms or graph theory through publications in proceedings of highly ranked international conferences and/or journals. Background in the specific areas of projects in question will be an advantage.

The gross annual salary is around 100,000PLN. For comparison, this translates to around twice the average salary in Poland. The position comes with a generous travel support and no teaching duties.

The application deadline is 10th September 2018. The starting date is flexible, but not earlier than 1st November 2018.

To apply, send a CV both to Marcin Pilipczuk (malcin@mimuw.edu.pl) and Piotr Sankowski (sank@mimuw.edu.pl). Please indicate your preference with regards to the project. Questions and informal inquiries are welcome.

Sweet and Sour News

This 'sweet and sour' news is already some time overdue. You might already know how a typical geographical distribution of ERC grants looks like. The next figure shows to which countries Consolidator grants went in 2017.

This distribution is usually typical for Poland, i.e., apx. 1 grant is given. This in general is rather 'sour' news. Still a 'sweet' information is that this was yet another grant in algorithms that went to our group in Warsaw. Hence, we currently have three ERC grants running:

1. Marcin Pilipczuk got ERC Starting Grant CUTACOMBS - Cuts and decompositions: algorithms and combinatorial properties,
2. Marek Cygan got ERC Starting Grant TOTAL - Technology transfer between modern algorithmic paradigms,
3. I, myself, got ERC Consolidator Grant TUGboAT - Towards Unification of Algorithmic Tools.

In other words, there are some interesting project happening right in Warsaw, and if you would like to visit us, just let us know.

ESA Test-of-Time Award 2017

Announcement of the ESA Test-of-Time Award 2017

European Symposium on Algorithms (ESA)

The ESA Test-of-Time Award (ESA ToTA) recognizes outstanding papers in algorithms research that were published in the ESA proceedings 19-21 years ago and which are still influential and stimulating for the field today. For the 2017 award, papers from ESA'96 to ESA'98 were considered.

The committee nominates the following paper for the ESA ToTA 2017. The paper stands out as a classic in the algorithms field and continues to be cited as an exemplary study in its field.

From ESA 96-98:

James Abello, Adam L. Buchsbaum, and Jeffery R. Westbrook
A Functional Approach to External Graph Algorithms
Proceedings ESA'98, pp. 332-343
also in: Algorithmica 32 (2002) 437-458

The paper deals with the design of algorithms that operate on massive data sets in external memory. Building on the well-known I/O model of complexity by Aggarwal and Vitter, the authors introduce a novel design principle for external algorithms based purely on functional transformations of the data, which facilitates standard checkpointing and program optimization techniques. Illustrated on a variety of graph problems, their approach is proved to be elegant and versatile in the design of both deterministic and randomized external algorithms while the resulting I/O complexities remain competitive. Functional algorithms are also designed for semi-external problems, in which the
nodes fit in main memory but the connecting edges are abundant and only available in external memory. The paper is an excellent illustration of how general principles of functional program design and model-based complexity can remain in harmony in the field of external algorithms.

Award Committee:
Giuseppe F. Italiano (Rome),
Mike Paterson (Warwick),
Jan van Leeuwen (Utrecht)


Some pictures from ICALP

On 10-13 July we hosted ICALP in Warsaw. It was fun! See a few random pictures below.


We in Warsaw, recently stumbled upon http://csrankings.org/ which ranks CS departments world-wide according to publication counts in mayor conferences. A cool aspect of this ranking is that one can set the year range for the counted publications. We rather only very recently, i.e., during the last 5-10, started doing well, so this parameter allows to track this change. As we are working mostly in theory let us restrict the ranking to theory only, i.e, Algorithms & complexity; Cryptography; Logic and verification. If you set the range to start in 2000 - to contain the last 15 years, then we are placed on position 10 world-wide. Quite cool already. Setting the starting point to 2005 bumps us to the 6th position. The most interesting part happens when you set the starting point to 2010, i.e., last 5 years, as you get the following table:

Rank Institution Average Count Faculty
1 University of Warsaw 8.4 24
2 Massachusetts Institute of Technology 8.2 20
3 University of Texas - Austin 7.3 8
4 Stanford University 7.1 12
5 Cornell University 6.9 14
6 Northeastern University 6.1 10
7 New York University 5.9 10
7 Carnegie Mellon University 5.9 14
9 University of Illinois at Urbana-Champaign 5.7 14
9 University of California - San Diego 5.7 10

Quite surprising... as all the ranking are usually. However, there might be some reasons for this. First of all, we cover all three areas that are counted in theory. For example, logic is visibly stronger in Warsaw than in other places included in top 10. Second, we indeed started doing quite well, e.g., we got 6 ERC grants so far. I do not really believe in rankings, but at least it is some indication that Warsaw is not such a bad place to be - see the cat meme.

Bratislava Declaration of Young Researchers

The Bratislava Declaration of Young Researchers is something I was involved in recently. Its preparation was inspired by Slovak Presidency of the EU and it was presented on today's informal Council of Ministers responsible for competitiveness (Research). I hope this will have some follow up, as current trend in funding research in EU is in my opinion (and not only my as this declaration shows) going in the wrong direction.

Why should you not use the automatic assignment by EasyChair

Some days ago I have assigned papers to my PC in ESA Track A. I tried to use automatic assignment in EasyChair and this was a rather disappointing experience. Just by running it I understood why some assignments I got as a PC member in previous conferences were so bad - they bad without any good reason. Let me explain what happened this time.

I clicked the automatic assignment button and I got a very unfair assignment. EasyChair wanted to punish 3 of my PC members by giving them 11, 12 and 15 papers from their No list. In EasyChair one can bid Yes, Maybe and No on papers. I found this rather absurd as 15 paper was more than half of the total review load. The question is: Does this poor guy need to get so many Nos in optimal assignment? The short intuitive answer is: most probably no, as there is a lot of freedom in each maximal size matching (by Gallai-Edmonds decomposition).

Hence, in 2 hours I coded my own assignment procedure. I assumed that in the assignment:

  • first, I want to maximize the number of papers assigned to Maybes and Yeses,
  • second, under the first assumption, I want to maximize the number of papers assigned Yeses.

This can be formalized as a maximum-cost maximum-flow problem:

  • connect the source vertex with each PC member with a zero cost edge of capacity equal to review load,
  • connect each PC member with each paper with edges of capacity 1 and cost 0 for No, 10000 for Maybe and 10001 for Yes.
  • connect each paper with the sink with edge of cost 0 and capacity 3.

I executed it and I got assignment with the same number of Nos - 80 and Maybes -100 as EasyChair. And of course, it was not much more fair than the one given by EasyChair. If you always wondered how EasyChair computes the assignment this is the way. Essentially, there is no reason for this to be fair in any sense. One is optimizing global cost, so it should be clear that locally it can be bad, e.g., some PC members will get bad assignments without any good reason. It can be even worse as one can be getting many Nos due to the execution order of procedure, as there is always a lot of freedom in the optimal matching. It can happen that even if you bid on almost everything you will get all the Nos if all people bid No on the same papers.

There is a solution here - I added third assumption to my procedure:

  • zero, no PC member can get more than X Nos, where X is a parameter.

This can be easily incorporated into the max-flow problem. One just needs to split a vertex representing each PC member into three vertices: PC_0, PC_No and PC_NotNo. The maximum-cost maximum-flow problem becomes:

  • connect the source vertex with all PC_0 vertices with a zero cost edge of capacity equal to review load,
  • connect PC_0 to PC_No with zero cost edge of capacity X,
  • connect PC_0 to PC_NotNo with zero cost edge of capacity equal to review load,
  • connect PC_No with edges of cost 0 to all papers with No,
  • connect PC_NotNo with each paper with edges of capacity 1 and cost 10001 for Maybe and 10001 for Yes.
  • connect each paper with sink with edge of cost 0 and capacity 3.

I executed it - the table below shows the number of Maybes in the assignment in dependence on the parameter X.

 X 4 5 6 7 8 9 10 11 12
 #Maybes 120 116 112 109 106 104 102 100 100

One striking thing is that there exists an optimal assignment where the poor guy that was getting 15 Nos is getting only 11 Nos. Essentially, there was no reason for giving 15 Nos to this PC member! This probably already happened to many of you ;). I the final assignment I went for X=4 as this actually meant that almost everyone gets 3 Nos and only 2 PC members get 4 Nos. This much fairer assignment costed only 20 Maybes in the quality, what I found a fair cost of being fairer.