Trimmed Moebius Inversion and Graphs of Bounded Degree

We study ways to expedite Yates's algorithm for computing the zeta and Moebius transforms of a function defined on the subset lattice. We develop a trimmed variant of Moebius inversion that proceeds point by point, finishing the calculation at a subset before considering its supersets. For an $n$-element universe $U$ and a family $scr F$ of its subsets, trimmed Moebius inversion allows us to compute the number of packings, coverings, and partitions of $U$ with $k$ sets from $scr F$ in time within a polynomial factor (in $n$) of the number of supersets of the members of $scr F$. Relying on an intersection theorem of Chung et al. (1986) to bound the sizes of set families, we apply these ideas to well-studied combinatorial optimisation problems on graphs of maximum degree $Delta$. In particular, we show how to compute the Domatic Number in time within a polynomial factor of $(2^{Delta+1-2)^{n/(Delta+1)$ and the Chromatic Number in time within a polynomial factor of $(2^{Delta+1-Delta-1)^{n/(Delta+1)$. For any constant $Delta$, these bounds are $O bigl((2-epsilon)^n bigr)$ for $epsilon>0$ independent of the number of vertices $n$.