47 research outputs found
The Tutte Polynomial of a Morphism of Matroids 5. Derivatives as Generating Functions of Tutte Activities
We show that in an ordered matroid the partial derivative
\partial^{p+q}t/\partialx^p\partialyq of the Tutte polynomial is p!q! times the
generating function of activities of subsets with corank p and nullity q. More
generally, this property holds for the 3-variable Tutte polynomial of a matroid
perspective.Comment: 28 pages, 3 figures, 5 table
The Tutte Polynomial of a Morphism of Matroids 6. A Multi-Faceted Counting Formula for Hyperplane Regions and Acyclic Orientations
We show that the 4-variable generating function of certain orientation
related parameters of an ordered oriented matroid is the evaluation at (x + u,
y+v) of its Tutte polynomial. This evaluation contains as special cases the
counting of regions in hyperplane arrangements and of acyclic orientations in
graphs. Several new 2-variable expansions of the Tutte polynomial of an
oriented matroid follow as corollaries.
This result hold more generally for oriented matroid perspectives, with
specific special cases the counting of bounded regions in hyperplane
arrangements or of bipolar acyclic orientations in graphs.
In corollary, we obtain expressions for the partial derivatives of the Tutte
polynomial as generating functions of the same orientation parameters.Comment: 23 pages, 2 figures, 3 table
10 Points in Dimension 4 not Projectively Equivalent to the Vertices of a Convex Polytope
AbstractUsing oriented matroids, and with the help of a computer, we have found a set of 10 points inR4 not projectively equivalent to the vertices of a convex polytope. This result confirms a conjecture of Larman [6] in dimension 4