The Morse-Conley complex is a central object in information compression in topological data analysis, as well as the application of homological algebra to analysing dynamical systems. Given a poset-graded chain complex, its Morse-Conley complex is the optimal chain-homotopic reduction of the initial complex that respects the poset grading.  In this work, we give a purely algebraic derivation of the Morse-Conley complex using homological perturbation theory. Unlike Forman’s discrete Morse theory for cellular complexes, our algebraic formulation does not require the computation of acyclic partial matchings of cells.  We show how this algebraic perspective also yields efficient algorithms for computing the Conley complex.  This talk features joint work with Álvaro Torras Casas and Ulrich Pennig in "Computing Connection Matrices of Conley Complexes via Algebraic Morse Theory" (arXiv:2503.09301). 
 

Given a triangulated 3-manifold, can we decide whether it is hyperbolic? In general, no efficient algorithm for answering this question is known; however, the problem becomes more manageable if we restrict our attention to specific classes of 3-manifolds. In this talk, I will discuss how to certify that a triangulated fibred 3-manifold is hyperbolic, in polynomial time in the size of the triangulation and in the Euler characteristic of the fibre. The argument relies on the theory of normal surfaces, as well as several previously known certification algorithms, of which I will give a survey. I will also mention, time permitting, a recent algorithm to decide if an element of the mapping class group of a surface is pseudo-Anosov in polynomial time, which is used in the certification procedure.

In this talk, I will discuss a model mixture of active (self-propelled) and passive (diffusive) particles with non-reciprocal effective interactions (or forces that violate Newton’s third law). We derive the hydrodynamic PDE limit for the particle densities, which is not a Wasserstein gradient flow of any free energy, consistent with the microscopic model having non-equilibrium steady states. We study the emergence of collective behaviour, which includes phase separation and dynamical (travelling) steady states.