Jakob Nordström / Open positions / Postdoc positions in combinatorial optimization

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Postdoctoral Positions in Combinatorial Optimization

The Department of Computer Science (DIKU) at the University of Copenhagen invites applications for postdoc positions in combinatorial optimization.

The Scientific Environment

We are looking for outstanding junior researchers with an innovative mind-set and intellectual curiosity to strengthen and complement the research profile of the Mathematical Insights into Algorithms for Optimization (MIAO) group headed by Jakob Nordström, which is active at both the University of Copenhagen and Lund University on either side of the Øresund Bridge.

The MIAO research group has a unique profile in that we are doing cutting-edge research both on the mathematical foundations of efficient computation and on state-of-the-art practical algorithms for real-world problems. This creates a very special environment, where we do not only conduct in-depth research on different theoretical and applied topics, but where different lines of research cross-fertilise each other and unexpected and exciting synergies often arise. Much of the activities of the group revolve around powerful algorithmic paradigms such as, e.g., Boolean satisfiability (SAT) solving, Gröbner basis computations, integer linear programming, and constraint programming. This leads to classical questions in computational complexity theory—though often with new, fascinating twists—but also involves work on devising clever algorithms that can exploit the power of such paradigms in practice.

We are fortunate to be part of the Algorithms and Complexity Section at DIKU, which is world-leading in algorithms and complexity theory (currently ranked 11th worldwide by CSrankings.org) and has a strong presence at top-tier TCS conferences like STOC, FOCS, and SODA as well as at premier AI venues like AAAI, IJCAI, and NeurIPS. DIKU hosts the Basic Algorithms Research Copenhagen (BARC) centre joint with the IT University of Copenhagen (ITU), and we also have extensive collaborations with the Technical University of Denmark (DTU) and with Lund University on the Swedish side of the Øresund Bridge, as well as with our many visitors. We aim to attract top talent from around the world to an ambitious, creative, collaborative, and fun environment. Using the power of mathematics, we strive to create fundamental breakthroughs in algorithms and complexity theory. While the focus in on foundational research, we do have a track record of surprising algorithmic discoveries leading to major industrial applications.

We currently have openings for both theoretically and practically inclined researchers. There is a lot of flexibility as to what kind of research to pursue, and all candidates are welcome, both those who want to go deep into either theory or practice and those who are inspired by the challenge of bridging the gap between the two.

On the theory side, most of our work is in proof complexity, which studies formal systems for reasoning about logic formulas and other types of problems. Proof complexity has connections to foundational questions in computational complexity theory, but also plays an important role in algorithm analysis by providing a rigorous understanding of the power and limitations of different algorithmic approaches. As often happens in theoretical computer science, our research has revealed deep, and often quite surprising, connections to other areas such as, e.g., circuit complexity, communication complexity, and hardness of approximation, and therefore researchers in these or other related areas are more than welcome to apply.

On the practical side, we are working on designing efficient algorithms for automated reasoning and combinatorial optimization, and on gaining a more rigorous scientific understanding of such algorithms. We are particularly interested in algorithms that can exploit sophisticated mathematical techniques to achieve exponential improvements in performance compared to the current state of the art—something that theoretical research suggests should be possible, but that has so far been hard to achieve in practice. Our most active line of work is focusing on combining ideas from SAT solving and mixed integer linear programming (MIP) to construct a new 0-1 integer linear programming solver RoundingSat. This solver is already world-leading when it comes to pseudo-Boolean solving, but our goal is to develop it further, integrating ideas also from MaxSAT solving, MIP solving, and possibly also satisfiability modulo theories (SMT) solving and constraint programming (CP), ultimately hoping to go significantly beyond the current state of the art.

Quite recently, we have also begun investigating, and have made research breakthroughs on, how to verify the correctness of state-of-the-art algorithms for automated reasoning and combinatorial optimization. Such algorithms are often highly complex, and even mature commercial solvers are known to sometimes produce wrong results. Our goal is to design a new generation of certifying solvers with so-called proof logging, meaning that the solvers output not only a solution but also a machine-verifiable proof that is easy to check and provides 100% formal guarantees that the claimed solution is correct. Our tool VeriPB can already support efficient proof logging for some solving techniques that have long remained beyond the reach of other tools, and we have recently received prestigious AAAI '22 distinguished paper and SAT '22 best paper awards for our work.

Job Description

These postdoc positions are full-time research positions for an expected duration of two years. Within the overall framework sketched above, the postdocs will be expected and encouraged to contribute to and influence the research agenda. Taking part in teaching graduate seminar courses is encouraged but not required. Travel funding is included, and the group also receives visitors on a regular basis.

The starting date is negotiable, but the default would be in August-September 2023.

The University of Copenhagen is currently expanding strongly in computer science. We expect to have tenure-track openings in in the coming years, and welcome postdoctoral researchers interested in exploring such opportunities.

Qualifications

Applicants should have or be about to receive a PhD degree in a subject relevant for the research area, and should have a passionate interest in research. The successful candidate is expected to have a solid background in computer science and mathematics, and should have a strong research record as witnessed by publications in top conferences such as AAAI, IJCAI, SAT, and CP, or in journals of comparable quality.

The working language of the group is English, and knowledge of English is also fully sufficient to navigate every-day life in Scandinavia in general. It might also be worth mentioning that Scandinavian countries routinely score at the absolute top in rankings of quality of life such as, e.g., the OECD Better Life Index.

Workplace

The University of Copenhagen was founded in 1479 and is the oldest and largest university in Denmark. It is often ranked as the best university in Scandinavia and consistently as one of the top places in Europe. Within computer science, it is ranked 2nd in the European Union (post-Brexit) by ShanghaiRanking.

Further information about the Department of Computer Science and the Faculty of Science can be found at www.science.ku.dk/english/about-the-faculty/organisation/.

Application

The application deadline is January 15, 2023 at midnight local time.

Applications must be submitted via the University of Copenhagen recruitment system. Please see the official advertisement for more details including a link to the application form.

The application should include the following documents:

1. Curriculum vitae.
2. Diplomas and transcripts of records (MSc/BSc and PhD degree or equivalent).
3. List of publications including links to the applicant's pages at DBLP and Google Scholar.
4. Brief research statement with description of research so far and future research goals and interests, and with a short description of 3 selected papers.
5. Copies of the above 3 selected papers.
6. Names and addresses for three references who might be contacted later in the recruitment process.

Please observe that all the documents above should be in English (or for official documents possibly in Danish).

The University of Copenhagen wishes for our staff to reflect the diversity of society and thus welcomes applications from all qualified candidates regardless of personal background.

Further Information and Contact Details

Inquiries about the positions can be made to Jakob Nordström at jn@di.ku.dk.