[grads] [Sem-coll] [Sem-Coll] AM/BCPS Colloquim: Monday, Nov 13 ---- AM Seminar: Friday, Nov 17

George Skountrianos skougeo at iit.edu
Thu Nov 9 13:23:56 CST 2006

Please join us for the Applied Mathematics/BCPS Colloquium on Monday, 
Nov 13 and Applied Mathematics Seminar on Friday Nov 17. Refreshments 
will be served 15 minutes prior to each talk.

AM/BCPS Colloquium: Monday, Nov 13 3:50pm, LS 111

Speaker: David Fernandez-Baca (Iowa State University )
Title: Spline Compatibility-Based Clustering of Phylogenetic Data Sets 

The treatment of conflict within data sets is among the most debated 
questions in phylogenetics, and it is an especially relevant concern 
with the accumulation of large data sets that combine data from many 
sources. Indeed, recent genomic-scale phylogenetic analyses have 
called attention to the extent of the variation in the phylogenetic 
signal among loci. This variation results from a several causes, 
including differing relative branch lengths, recombination, and 
horizontal gene transfer. Regardless of its source, identifying 
phylogenetic conflict is an important step in building reliable 
evolutionary trees.

We describe a method to partition phylogenetic data sets of discrete 
characters based on the pairwise compatibility of characters. Unlike 
previous approaches, our method requires no knowledge of the 
phylogeny, model of evolution, or characteristics of the data. The 
method is based on a similarity scoring scheme that measures how close 
pairs of characters are to compatibility. The goal is to partition the 
characters into clusters so that characters within a cluster are more 
compatible with each other than they are with characters in other 
clusters. While partitioning according to these criteria is 
computationally intractable, we show that spectral methods quickly 
provide high-quality solutions. We demonstrate that our partitioning 
method effectively identifies conflicting phylogenetic signals in 
simulated and empirical data sets. 

This is joint work with Duhong Chen, of the Department of Computer 
Science, Iowa State University, and J. Gordon Burleigh, of the Section 
of Evolution and Ecology, University of California, Davis. 

AM Seminar: on Friday, Nov 17 3:15pm, E1 119

Speaker: Bridget Tenner (Massachusetts Institute of Technology)
Title: Reduced Decompositions and Permutation Patterns 

Billey, Jockusch, and Stanley characterized 321-avoiding permutations 
by a property of their reduced decompositions. We generalize that 
result with a study of permutations via their reduced decompositions 
and the notion of pattern containment. These techniques are used to 
prove a new characterization of vexillary permutations in terms of 
their principal dual order ideals in a particular poset. Additionally, 
the combined frameworks yield several new results about the 
commutation classes of a permutation. In particular, these describe 
structural aspects of the corresponding graph of the classes and the 
zonotopal tilings of a polygon defined by Elnitsky that is associated 
with the permutation. 

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