Rank jumps in Codimension 2 A-Hypergeometric Systems
arXiv:math/0009148
Abstract
The holonomic rank of the A-hypergeometric system H_A(β) is shown to depend on the parameter vector βwhen the underlying toric ideal I_A is a non Cohen Macaulay codimension 2 toric ideal. The set of exceptional parameters is usually infinite.
24 pages