Containment Counterexamples for ideals of various configurations of points in ${\bf P}^N$

Abstract

When $I$ is the radical homogeneous ideal of a finite set of points in projective $N$-space, ${\bf P}^N$, over a field $K$, it has been conjectured that $I^{(rN-N+1)}$ should be contained in $I^r$ for all $r\geq 1$. Recent counterexamples show that this can fail when N=r=2. We study properties of the resulting ideals. We also show that failures occur for infinitely many $r$ in every characteristic $p>2$ when N=2, and we find additional positive characteristic failures when $N>2$.