Simplicial Convolutional Filters

IEEE Transactions on Signal Processing, vol. 70, pp. 4633–4648

Abstract

We study linear filters for processing signals supported on abstract topological spaces modeled as simplicial complexes, which may be interpreted as generalizations of graphs that account for nodes, edges, triangular faces, etc. To process such signals, we develop simplicial convolutional filters defined as matrix polynomials of the lower and upper Hodge Laplacians. First, we study the properties of these filters and show that they are linear and shift-invariant, as well as permutation and orientation equivariant. These filters can also be implemented in a distributed fashion with a low computational complexity, as they involve only (multiple rounds of) simplicial shifting between upper and lower adjacent simplices. Second, focusing on edge-flows, we study the frequency responses of these filters and examine how we can use the Hodge-decomposition to delineate gradient, curl and harmonic frequencies. We discuss how these frequencies correspond to the lower- and the upper-adjacent couplings and the kernel of the Hodge Laplacian, respectively, and can be tuned independently by our filter designs. Third, we study different procedures for designing simplicial convolutional filters and discuss their relative advantages. Finally, we corroborate our simplicial filters in several applications: to extract different frequency components of a simplicial signal, to denoise edge flows, and to analyze financial markets and traffic networks.

Authors 4

1. Maosheng Yang

   Delft University of Technology

   Affiliation as printed

   Department of Intelligent Systems, Delft University of Technology, Delft, Netherlands

2. Elvin Isufi

   Delft University of Technology

   Affiliation as printed

   Department of Intelligent Systems, Delft University of Technology, Delft, Netherlands

3. Michael T. Schaub Aachen Department of Computer Science

   RWTH Aachen University

   Affiliation as printed

   Department of Computer Science, RWTH Aachen University, Aachen, Germany

   Dept. of Computer Science, RWTH Aachen University, Aachen, Nordrhein, Germany

4. Geert J. T. Leus

   Delft University of Technology

   Affiliation as printed

   Department of Microelectronics, Delft University of Technology, Delft, Netherlands

   Dept. of Microelectronics, Delft University of Technology, Delft, Zuid-Holland, Netherlands