Computing Generalized Ranks of Persistence Modules via Unfolding to Zigzag Modules
<|reference_start|>Computing Generalized Ranks of Persistence Modules via Unfolding to Zigzag Modules: For a $P$-indexed persistence module ${\sf M}$, the (generalized) rank of ${\sf M}$ is defined as the rank of the limit-to-colimit map for the diagram of vector spaces of ${\sf M}$ over the poset $P$. For $2$-parameter persistence modules, recently a zigzag persistence based algorithm has been proposed that takes advantage of the fact that generalized rank for $2$-parameter modules is equal to the number of full intervals in a zigzag module defined on the boundary of the poset. Analogous definition of boundary for $d$-parameter persistence modules or general $P$-indexed persistence modules does not seem plausible. To overcome this difficulty, we first unfold a given $P$-indexed module ${\sf M}$ into a zigzag module ${\sf M}_{ZZ}$ and then check how many full interval modules in a decomposition of ${\sf M}_{ZZ}$ can be folded back to remain full in a decomposition of ${\sf M}$. This number determines the generalized rank of ${\sf M}$. For special cases of degree-$d$ homology for $d$-complexes, we obtain a more efficient algorithm including a linear time algorithm for degree-$1$ homology in graphs.<|reference_end|>
@article{dey2024computing,
    title={Computing Generalized Ranks of Persistence Modules via Unfolding to
  Zigzag Modules},
    author={Tamal K. Dey and Cheng Xin},
    journal={arXiv preprint arXiv:2403.08110},
    year={2024},
    archivePrefix={arXiv},
    eprint={2403.08110},
    primaryClass={math.AT cs.CG}
}