International Mathematics Research Notices (2008) Vol. 2008 : article ID rnn081, 19 pages, doi:10.1093/imrn/rnn081
published on
July 24, 2008
© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
A Formula for Plücker Coordinates Associated with a Planar Network
Kelli Talaska
Department of Mathematics, University of Michigan, Ann Arbor, MI 48109, USA
Correspondence: Correspondence to be sent to: kellicar{at}umich.edu
For a planar directed graph G, Postnikov's boundary measurement map sends positive weight functions on the edges of G onto the appropriate totally non-negative Grassmann cell. We establish an explicit formula for Postnikov's map by expressing each Plücker coordinate as a ratio of two combinatorially defined polynomials in the edge weights, with positive integer coefficients. In the non-planar setting, we show that a similar formula holds for special choices of Plücker coordinates.

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