Soren Lassen

Work Experience

11/2004 - present   Software Engineer at Google Inc., Mountain View, CA.

7/2003 - 10/2004   Senior Member of Technical Staff at Riverbed Technology, San Francisco, CA.

Riverbed is a networking product company that develops software and network acceleration appliances that fuse compression, caching, and protocol transaction prediction technologies.

• Designed and implemented data compression, caching, storage, indexing, and hashing algorithms and data structures and network protocols in C++. Improved algorithms and protocols for robustness and data integrity. Increased data compression and throughput performance.
• Technical lead for the compression, storage, and event system infrastructure software.
• Designed and led the implementation of cross-cutting architectural improvements to optimize data buffering and optimize end-to-end operation latencies over low-bandwidth WAN connections. This work included changes to the Linux kernel TCP stack to fine-tune application software control over TCP socket buffers.
• Contributor to the hardware design and hardware evaluation for the appliance platforms.
• Ported all userspace software from x86 to AMD64 to support large amounts of main memory.
• Key contributor to the design, implementation, and testing of the company's initial Steelhead product release in May 2004.

12/1999 - 7/2003   Lead Architect and Senior Researcher at Digital Fountain, Fremont, CA.

Digital Fountain is a networking technology and product company, providing fast, predictable and scalable data delivery solutions based on proprietary forward error correction (FEC) codes.

• Invented, mathematically analyzed, and implemented Digital Fountain's latest-generation state-of-the-art scalable FEC algorithms with provably low error probability and computational complexity. The implementation is cross-platform and optimized for systems ranging from multi-processor servers to handheld and embedded devices. The resulting software libraries are in production use today, both internally and at the company's largest licensing partners.
• Designed the architecture of FEC encoding and decoding engines across Digital Fountain's server appliances and client software. These multi-threaded engines are C++, C, and Java programs employing scalable networking and disk I/O.
• Constructed FEC-based network protocols for both streaming media and static content delivery across both multicast and unicast IP networks. These protocols have solved numerous problems on the cutting-edge of IP networks, ranging from the reliable, on-demand delivery of streaming media to literally millions of concurrent users to the high-throughput, reliable point-to-point and point-to-multipoint delivery of very large files over lossy, high-latency unicast networks.
• Collaborated closely with many distinguished scientists, including colleagues CTO Mike Luby and Chief Scientist Professor Amin Shokrollahi, and affiliated scientists Professor Richard Karp, Professor Avi Wigderson, and IBM Researcher Hugo Krawczyk.
• Authored and co-authored patent applications about FEC codes, server and client system architecture, media distribution, and data transports.

1/1998 - 12/1999   Research Associate at University of Cambridge Computer Laboratory, UK.

Worked on the UK EPSRC research project "An Operational Theory of Objects" in collaboration with Professor Andrew Pitts and Senior Microsoft Researcher Andrew Gordon.

• Developed programming language theories and proof methods for a wide range of object oriented, imperative, functional, and non-deterministic programming concepts, based on operational semantics.
• Contributed to a new underlying calculus for the Action Semantics framework for semantic descriptions of programming languages.
• Collaborated and co-authored research papers with many academic and Microsoft researchers. The work was presented at programming language theory and software engineering conferences and published in international journals.

1991 - 1999   Teaching Assistant at the Computer Science and Mathematics departments at University of Aarhus, Denmark, and University of Cambridge Computer Laboratory, UK.

• Taught and supervised students on numerous undergraduate and graduate mathematics and computer science courses.

1988 - 1989   Software engineer at Purup Electronics, Aarhus, Denmark.

Purup Electronics was an industry leader in systems for design and high-precision printing of graphics and images for the pre-press industry.

• Developed graphical design software for graphical workstations used in the prepress industry. Architected and developed a solution for graphical security design (bank notes, legal documents, etc) in Fortran and 68000 assembly.

1986 - 1987   Military service, Jutland Transportation Regiment, Denmark.

Education

• Ph.D., Computer Science, University of Aarhus, Denmark, 1998.
• M.S., Computer Science, University of Aarhus, 1995.
• B.S., Computer Science & Mathematics & Classical Studies, University of Aarhus, 1993.

Publications

• Relational Reasoning about Functions and Nondeterminism. Department of Computer Science, University of Aarhus. BRICS Dissertation Series DS-98-2, 1998.

• Gavin Horn, Per Knudsgaard, Soren Lassen, Michael Luby, and Jens Eilstrup Rasmussen. A Scalable and Reliable Paradigm for Media on Demand, in IEEE Computer 34(9): 40-45, 2001.
• Andrew Gordon, Paul Hankin, and Soren Lassen. Implementation and Equivalence of Imperative Objects, in Journal of Functional Programming 9(4): 373-427, 1999.
• Soren Lassen. Relational Reasoning about Contexts, in Higher Order Operational Techniques in Semantics. Cambridge University Press 1998.
• Soren Lassen. Action Semantics Reasoning about Functional Programs, in Mathematical Structures in Computer Science 7(5): 557-589, 1997.

• Soren Lassen and Paul Blain Levy. "Typed Normal Form Bisimulation". 16th EACSL Annual Conference on Computer Science and Logic, CSL 07. (Lausanne, Switzerland, September 11-15, 2007.) Lecture Notes in Computer Science, Volume 4646, pages 283-297. Springer 2007.
• Kristian Støvring and Soren Lassen. "A complete, co-inductive syntactic theory of sequential control and state". 34th Annual ACM SIGPLAN Symposium on Principles of Programming Languages, POPL 2007. (Nice, France, January 17-19, 2007.) ACM SIGPLAN Notices 42(1): 161-172, 2007.
• Soren B. Lassen. "Head normal form bisimulation for pairs and the λμ-calculus (Extended Abstract)". 21st Annual IEEE Symposium On Logic In Computer Science, LICS 2006. (Seattle, USA, August 12-15, 2006.) IEEE press 2006, pages 297-306.
• Soren Lassen. "Eager Normal Form Bisimulation". 20th Annual IEEE Symposium On Logic In Computer Science, LICS 2005. (Chicago, USA, June 26-29, 2005.) IEEE press 2005, pages 345-354.
• Soren Lassen. "Normal Form Simulation for McCarthy's amb". 21st Annual Conference on Mathematical Foundations of Programming Semantics, MFPS XXI. (Birmingham, UK, May 18-21, 2005.) Electronic Notes in Theoretical Computer Science, Volume 155, pages 445-465. Elsevier 2006.
• Andrew Moran, Soren Lassen, and Simon Peyton Jones. "Imprecise Exceptions, Co-Inductively". 3rd International Workshop on Higher Order Operational Techniques in Semantics, HOOTS '99. (Paris, France, September 30 - October 1, 1999.) Electronic Notes in Theoretical Computer Science, Volume 26, pages 122-141. Elsevier 1999.
• Soren Lassen and Andrew Moran. "Unique Fixed Point Induction for McCarthy's Amb". Mathematical Foundations of Computer Science 1999, 24th International Symposium, MFCS '99. (Szklarska Poreba, Poland, September 6-10, 1999.) Lecture Notes in Computer Science, Volume 1672, pages 198-208. Springer 1999.
• Soren Lassen: "Bisimulation in untyped lambda calculus: Boehm trees and bisimulation up to context". 15th Conference on the Mathematical Foundations of Programming Semantics, MFPS XV. (Tulane University, New Orleans, LA, April 28 - May 1, 1999.) Electronic Notes in Theoretical Computer Science, Volume 20, pages 346-374. Elsevier 1999.
• Andrew Gordon, Paul Hankin, Soren Lassen: "Compilation and Equivalence of Imperative Objects". Foundations of Software Technology and Theoretical Computer Science, 17th Conference. (Kharagpur, India, December 18-20, 1997.) Lecture Notes in Computer Science, Volume 1346, pages 74-87. Springer 1997.

• Soren Lassen, Peter Mosses, and David Watt. "Introduction to AN-2: The Proposed New Version of Action Notation". 3rd International Workshop on Action Semantics, AS 2000. (Centre for Informatics, UFPE, Recife, Brazil, May 15-16, 2000.) BRICS Notes Series NS-00-6, pages 19-36.
• Soren Lassen. "An Algebra of Actions". 2nd International Workshop on Action Semantics, AS '99. (Amsterdam, The Netherlands, 21 March 1999.) BRICS Notes Series NS-99-3, pages 89-109.
• Soren Lassen and Corin Pitcher. "Similarity and Bisimilarity for Countable Non-Determinism and Higher-Order Functions". 2nd Workshop on Higher Order Operational Techniques in Semantics. (Center for the Study of Language and Information, Stanford University, USA. December 8-11, 1997.) Electronic Notes in Theoretical Computer Science, Volume 10. Elsevier 1997.
• Soren Lassen. "Design and Semantics of Action Notation". 1st International Workshop on Action Semantics, AS '94. (University of Edinburgh, Scotland, April 14, 1994.) BRICS Notes Series NS-94-1, pages 16-33.

Invited talks

• "Trees and bisimulation for the pure lambda-calculus". 3rd International Workshop on Higher Order Operational Techniques in Semantics, HOOTS '99. Paris, France. September 30 and October 1, 1999.

Some other talks

• "Divergence-Least Semantics Of amb Is Hoare", with Paul Blain Levy and Prakash Panangaden. Short presentation at 3rd APPSEM II Workshop (APPSEM05). Frauenchiemsee, Germany. September 12-15, 2005.
• "Bisimulation up to Context for Sequential Higher-Order Languages". The Semantic Challenge of Object-Oriented Programming, Dagstuhl Seminar 98261. Schloss Dagstuhl, Wadern, Germany. June 28 - July 3, 1998.
• "Operational Reasoning in Action Semantics". Workshop on Higher Order Operational Techniques in Semantics. Isaac Newton Institute for Mathematical Sciences, University of Cambridge, UK. October 28-30, 1995.
• "Action Theory". Workshop Logic, Domains, and Programming Languages. Fachbereich Mathematik, Technische Hochschule Darmstadt, Germany. May 25-27, 1994.

Patents and patent applications

• Amin Shokrollahi, Soren Lassen, and Richard Karp. Systems and processes for decoding chain reaction codes through inactivation. US Patent 6,856,263, February 15, 2005. US Patent 7,030,785, April 18, 2006. US Patent 7,265,688, September 4, 2007.
• Jens Rasmussen, Amin Shokrollahi, Soren Lassen, Gavin Horn, Vivek Goyal, Barry Dobyns, and Michael Luby. Systems and method for reliably communicating the content of a live data stream. US Patent 7,249,291, July 24, 2007.
• Gavin Horn, Michael Luby, Jens Rasmussen, Per Knudsgaard, and Soren Lassen. Methods and apparatus for scheduling, serving, receiving media-on-demand for clients, servers arranged according to constraints on resources. US Patent 7,240,358, July 3, 2007.
• Soren Lassen, Gavin Horn, Jeffrey Persch, Armin Haken, and Michael Luby. Scheduling of multiple files for serving on a server. US Patent 7,072,971, July 4, 2006.
• Amin Shokrollahi, Soren Lassen, and Michael Luby. Multi-stage code generator and decoder for communication systems. US Patent 7,068,729, June 27, 2006.
• David Tze-Si Wu, Soren Lassen, Kartik Subbana, Nitin Gupta, and Vivasvat Keswani. Automatic framing selection. International Patent Application PCT/US2006/029181, July 26, 2006.
• Michael Luby, Matt Doucleff, Avi Wigderson, and Soren Lassen. FEC-based reliability control protocols. US Patent Application 20050226272, October 13, 2005.
• Amin Shokrollahi and Soren Lassen. Systems and processes for fast encoding of Hamming codes. US Patent Application 20050010847, January 13, 2005.

Awards

• Danish Science Foundation Scholarship, 1995.
• University of Aarhus Research Foundation Grant, 1993.

Professional activities

• Paper reviewer for SIGCOMM and many programming language conferences and journals, including Annals of Pure and Applied Logic, Information and Computation, Theoretical Computer Science, Higher-Order and Symbolic Computation, POPL, LICS, ICFP, ESOP, CAAP, MFCS, SOS, HLCL, and HOOTS.
• Member of IEEE, IEEE Computer Society, ACM, and ACM SIGPLAN.

Other

Interests include politics, history, literature, and languages, both ancient and modern.

I live in San Francisco with my wife and two children, age 10 and 12, and two cats.