  In this paper, we study the strength of aggregation cuts for sign-pattern
integer programs (IPs). Sign-pattern IPs are a generalization of packing IPs
and are of the form $\{x\in \mathbb{Z}^n_+\ | \ Ax\le b\}$ where for a given
column $j$, $A_{ij}$ is either non-negative for all $i$ or non-positive for all
$i$. Our first result is that the aggregation closure for such sign-pattern IPs
can be 2-approximated by the original 1-row closure. This generalizes a result
for packing IPs. On the other hand, unlike in the case of packing IPs, we show
that the multi-row aggregation closure cannot be well approximated by the
original multi-row closure. Therefore for these classes of integer programs
general aggregated multi-row cutting planes can perform significantly better
than just looking at cuts from multiple original constraints.
