Block Triangular Preconditioners for Double Saddle-Point Linear Systems Arising in the Mixed Form of Poroelasticity Equations

In this paper, we study a class of inexact block triangular preconditioners for double saddle-point symmetric linear systems arising from the mixed finite element and mixed hybrid finite element discretization of Biot's poroelasticity equations. We extend the theoretical results presented in [Balani et al., NLAA 2024] for general double saddle-point problems with nonzero diagonal blocks, by developing a novel spectral analysis of the preconditioned matrix. This shows that the complex eigenvalues