Combinatorial Potlatch 2010
Western Washington University
Saturday, December 11, 2010

About the Combinatorial Potlatch

The Combinatorial Potlatch is an irregularly scheduled, floating, one-day conference. It has been held for many years at various locations around Puget Sound and southern British Columbia, and is an opportunity for combinatorialists in the region to gather informally for a day of invited talks and conversation. While most who attend work in, or near, the Puget Sound basin, all are welcome.  Typically there are three talks given by speakers who are visiting or new to the area, along with breaks for coffee and lunch. Many participants remain for dinner at a local restaurant or pub.

The American Heritage Dictionary defines "potlatch" as: A ceremonial feast among certain Native American peoples of the northwest Pacific coast, as in celebration of a marriage or an accession, at which the host distributes gifts according to each guest's rank or status. Between rival groups the potlatch could involve extravagant or competitive giving and destruction by the host of valued items as a display of superior wealth. [Chinook Jargon, from Nootka p'achitl, to make a potlatch gift.]

This fall's Potlatch is being hosted by the Department of Mathematics at Western Washington University in Bellingham, Washington on Saturday, December 11, 2010.

More info, including a history and links to previous Potlatches, is at The Combinatorial Potlatch Home Page.


All talks will be held in Biology 234, with registration and breaks nearby. See the Getting There section for exact locations and directions.

  • 10:00 AM Registration and Coffee
  • 11:00 AM Christine Kelley, Codes From Algebraic Lifts of Graphs
  • 12:00 PM Lunch
  • 2:00 PM Richard Guy, Some Columns Martin Gardner Might Have Written
  • 3:00 PM Cookies, Coffee and Cokes
  • 3:30 PM Welcome, Catherine Riordan, WWU Provost
  • 3:40 PM Kai-Uwe Schmidt, What's Special About 0.3420...? How to Increase the Merit Factor of Binary Sequences
  • 4:40 PM Happy Hour, Dinner

Talks and Abstracts

Christine Kelley, University of Nebraska, Lincoln

Codes From Algebraic Lifts of Graphs

Low-Density Parity-Check (LDPC) codes are characterized by having sparse parity-check matrices that may naturally be represented using sparse bipartite graphs. LDPC codes have gained widespread importance due to their simple graph-based decoding algorithms and simultaneous good (capacity-approaching) performance. One design strategy is to construct these codes by taking random lifts of a suitable base graph, yielding the family of "protograph codes." In this talk, we will discuss how the theory of voltage graphs can be used to obtain an algebraic construction of codes from graph lifts. We will discuss the known relationships between the base voltage graph and the code corresponding to the graph lift, and present several open problems in this direction.

Richard Guy, University of Calgary

Some Columns Martin Gardner Might Have Written

A collection of combinatorial curiosities: building Barrycades, constructing corrals, completing cubes, locating lighthouses, seeking subprime sequences, and maybe more.

Kai-Uwe Schmidt, Simon Fraser University

What's Special About 0.3420...? How to Increase the Merit Factor of Binary Sequences

The merit factor of a binary sequence measures the collective smallness of its aperiodic autocorrelations. The problem of determining the largest possible merit factor of long binary sequences has a long history and has been studied by mathematicians, theoretical physicists, and communications engineers. There exists an infinite family of binary sequences that achieves an asymptotic merit factor of 6, a result that dates back to 1988 and has been conjectured to be best possible. But in 2004, it was argued that, by a modification of this sequence family, the merit factor of long sequences can be increased from 6 to at least 6.34. However a proof that this is true for arbitrarily long sequences has not yet been found. I will review this construction and will then show that a similar construction applied to arbitrarily long m-sequences increases the merit factor from 3 to at least 3.34.


The Combinatorial Potlatch has no sponsoring organization and no budget. And we like it that way. Consequently, there are no registration fees because we wouldn't know what to do with them. You are on your own for meals and lodging, speakers travel at their own expense and the host institution provides facilities and food for the breaks. So expressions of appreciation to the speakers and the hosts are preferred and especially encouraged. Thanks.

However this year, we do need to select entrees for lunch in advance, so please read the dining section and email your selection in advance.

Getting There

All talks will be held in Biology 234 (building 42 on both the parking and the campus maps). Parking lot 12A is about a 3 to 5 minute walk away and there is no charge.

Driving Directions and WWU Campus Map [PDF]
Parking Map [PDF]

Airport Shuttle: Sea-Tac Airport to Bellingham

General Information for Visitors


Places to Stay: from the WWU Admission Office

Best Western Lakeway Inn: next to I-5, about 1.5 miles to WWU

Bellingham Guesthouse Inn: Same location as Lakeway Inn

Dining and Happy Hour

No-Host Lunch: We have arranged lunch at Giuseppe's. Please email your choice of entree to Amites Sarkar at amites.sarkar (at) wwu (dot) edu as soon as possible, as we need to let the restaurant know the selections in advance.

  • Antipasti: Bruschetta della Casa (Toasted baguette topped with fresh tomato, onion garlic, basil, gorgonzola and extra virgin olive oil)
  • Side salad: Mixed baby greens, tomato, olive; dressed with balsamic vinaigrette; garnished with gorgonzola
  • Entree: Choice of
    1. Ravioli della Nonna (Cheese ravioli with sauteed mushroom and garlic served in a creamy, tomato pesto sauce)
    2. Pollo alla Parmigiana (Oven baked chicken with marinara, mozzarella and parmesan; served with spaghettini)
    3. Meat Lasagna
  • Dessert: Spumoni gelato

The cost for lunch is $23, which includes tax and service charge.

No-Host Happy Hour and Dinner: At the Copper Hog.

WWU Admission Office: Places to Eat


  • Rob Beezer, University of Puget Sound, beezer (at) ups (dot) edu, Communications Chair
  • Nancy Ann Neudauer, Pacific University, nancy (at) pacificu (dot) edu, Program Chair
  • Amites Sarkar, Western Washington University, amites.sarkar (at) wwu (dot) edu, Local Arrangements Chair
Last updated: November 28, 2010,