This package computes the minimal resolution of the Stanley-Reisner ring of the boundary complexes Δ(d,m) of cyclic polytopes of dimension d on m vertices using unprojection theory.
We implement the results of
J. Boehm, S. Papadakis: On the structure of Stanley-Reisner rings associated to cyclic polytopes, http://arxiv.org/abs/0912.2152
connecting Stanley-Reisner rings and unprojection to give a formula for the minimal resolutions.
The algorithm given there is applied in the function cycRes and computes the minimal resolution inductively starting from Koszul complexes. The function cycRes has an Option verbose to output the unprojection structure of the minimal resolution.
We also compute the minimal resolution of a flat family in which the Stanley-Reisner ring is the special fiber, see cycResDef.
In addition to this, the package exports functions to compute the Stanley-Reisner ideal of Δ(d,n), hence allowing the user to compare the result of cycRes with the resolution computed by the M2 command resolution via Groebner bases.
The theoretical concept implemented here is an instance of a new relationship between algebra and combinatorics via unprojection theory (so in some sense birational geometry), which also shows up in
J. Boehm, S. Papadakis: Stellar subdivisions and Stanley-Reisner rings of Gorenstein complexes, http://arxiv.org/abs/0912.2151
in a different flavor, but is probably applicable in a more general setting.
Key functions and data types:
The central function of the package is:
cycRes -- Compute the cyclic polytope minimal resolution via unprojection
Other important types and functions:
cycResDef -- Compute the minimal resolution of the unprojection deformation of a cyclic polytope
Complex -- The class of all simplicial complexes
Face -- The class of all faces of simplicial complexes
complexToIdeal -- Compute the Stanley-Reisner ideal associated to a simplicial complex
idealToComplex -- Compute the Stanley-Reisner complex associated to a monomial square free ideal
delta -- The boundary complex of a cyclic polytope
Examples:
Codimension 4 cyclic polytopes
The following examples contain detailed output of all objects of the construction:
Codimension 4 cyclic polytopes with details
A codimension 3 example with details
A codimension 5 example with details
Installation:
Put the file CyclicPolytopeRes.m2 somewhere into the path of Macaulay2 (usually into the directory .Macaulay2/code inside your home directory, type path in M2 to see the path) and do inside M2
installPackage "CyclicPolytopeRes"