nLab persistent homotopy



Homotopy theory

homotopy theory, (∞,1)-category theory, homotopy type theory

flavors: stable, equivariant, rational, p-adic, proper, geometric, cohesive, directed

models: topological, simplicial, localic, …

see also algebraic topology



Paths and cylinders

Homotopy groups

Basic facts




Persistent homotopy studies homotopy types (of topological spaces) as a parameter varies, hence filtered homotopy types (of filtered topological spaces), with focus on which elements of homotopy groups at given stage persist how far through the filtering to later stages. A key application is to Vietoris-Rips complexes of discrete subsets in a metric space.

Notably in topological data analysis (TDA) these VR complexes arise as “point clouds” of datapoints, and the corresponding persistent homotopy is thought to detect relevant structure hidden in such data. As such, persistent homotopy refines the traditional use of persistent homology in TDA.

In general, persistent homotopy theory is to persistent homology as homotopy theory is to homology theory: homotopy is a finer invariant than homology, the former sees the full homotopy type of a topological space, the latter at most the underlying stable homotopy type.

In other words, homology involves a kind of linearization or abelianization which loses information that is retained in the homotopy type (see the Hurewicz theorem). Therefore persistent homotopy is in general a finer invariant of filtered topological spaces than persistent homology. In fact, traditional persistent homology considers only ordinary homology which is the coarsest of all generalized homology invariants. Hence in between the coarse invariant of persistent homology and the fine invariants of persistent homotopy will be intermediate invariants that would deserve to be called persistent generalized homology – but these have not yet found much attention, certainly not in the context of topological data analysis.

However, besides homology there is, dually, also cohomology, whose analogous homotopy theoretic refinement is (non-abelian cohomology theories, but in particular:) co-homotopy. The generalization of cohomotopy to the context of persistence lends itself to the analysis of persistence of level sets of continuous functions: see at persistent cohomotopy (and see the references below).

homologyordinary homologygeneralized homologyhomotopy
cohomologyordinary cohomologygeneralized cohomologycohomotopy
persistent homologypersistent ordinary homologypersistent generalized homologypersistent homotopy
persistent cohomologypersistent ordinary cohomologypersistent generalized cohomologypersistent cohomotopy



Original articles with focus on establishing the homotopy-version of the stability theorem and the persistent version of Whitehead's theorem:


Further discussion:

Discussion with focus on the van Kampen theorem, excision and the Hurewicz theorem in persistent homotopy:

  • Mehmet Ali Batan, Mehmetcik Pamuk, Hanife Varli, Persistent Homotopy [[arXiv:1909.08865]]

Cohomotopy in topological data analysis

Introducing persistent cohomotopy as a tool in topological data analysis, improving on the use of well groups from persistent homology:


Last revised on July 17, 2022 at 05:35:31. See the history of this page for a list of all contributions to it.