Simplifying modular lattices by removing doubly irreducible elements
Jukka Kohonen
TL;DR
The work introduces a structural reduction for modular lattices by removing selected doubly irreducible elements (trinkets) to form racks, enabling compact representations of the large family of unlabeled vertically indecomposable modular lattices ($\mathrm{MV}_n$). It establishes that racks preserve key properties and can be decorated to recover the full lattices, with ornamentation counted via Polya enumeration using cycle indices. The authors perform extensive computations up to $n\le 40$, producing a virtual listing of $\mathrm{MV}_n$ and an accompanying explicit count of all modular lattices, and provide SageMath tools for on-demand generation and sampling. This approach yields dramatic storage savings (over 3000x) and scalable access to large lattice families, while offering a pathway to further optimization through gluing and database-style querying. The work combines structural theory, exhaustive computation, and software to make large-scale lattice data more tractable and usable for researchers.
Abstract
Lattices are simplified by removing some of their doubly irreducible elements, resulting in smaller lattices called racks. All vertically indecomposable modular racks of $n \le 40$ elements are listed, and the numbers of all modular lattices of $n \le 40$ elements are obtained by Pólya counting. SageMath code is provided that allows easy access both to the listed racks, and to the modular lattices that were not listed. More than 3000-fold savings in storage space are demonstrated.
