swartz@watdcsu.waterloo.edu ( SWARTZ SJ - COMBINATORICS Swartz OPT. ) (09/25/89)
C & O SEMINAR
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|DATE: Friday, September 29, 1989 |
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|TIME: 3:30 p.m. |
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|PLACE: MC5158 |
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|SPEAKER: Dr. David Wagner |
| University of Waterloo |
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|TITLE: Total Positivity in Combinatorics |
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ABSTRACT
Total positivity is a strong condition on a
matrix with many applications in analysis. A deep
theorem due to Aissen, Edrei, Schoenberg and Whitney
characterizes the generating functions of totally
positive Toeplitz matrices. We will discuss this
result and applications of it to two kinds of generat-
ing functions which arise in enumerative combinator-
ics: partition polynomials of set systems, and order
polynomials of partially ordered sets. In particular
we will establish log-concavity of many combinatorial
sequences.
September 22, 1989