[grads] [Sem-coll] Correction to Monday, Nov 13 Joint colloquium

Robert Ellis rellis at math.iit.edu
Sun Nov 12 23:13:15 CST 2006

The AM/BCPS colloquium Monday will start at 3:45, with coffee at 3:35. 
Sorry for the confusion.  The Friday seminar talk is listed correctly.

AM/BCPS Colloquium: Monday, Nov 13 ***3:45pm***, 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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