Resolutions of Ideals of Uniform Fat Point Subschemes of P^2

Brian Harbourne, Sandeep Holay, Stephanie Fitchett

Published 1999-06-18Version 1

Let I be the ideal corresponding to a set of general points $p_1,...,p_n \in P^2$. There recently has been progress in showing that a naive lower bound for the Hilbert functions of symbolic powers $I^{(m)}$ is in fact attained when n>9. Here, for m sufficiently large, the minimal free graded resolution of $I^{(m)}$ is determined when n>9 is an even square, assuming only that this lower bound on the Hilbert function is attained. Under ostensibly stronger conditions (that are nonetheless expected always to hold), a similar result is shown to hold for odd squares, and for infinitely many m for each nonsquare n bigger than 9. All results hold for an arbitrary algebraically closed field k.