Decoupling multistep schemes for elliptic–parabolic problems

We study the construction and convergence of decoupling multistep schemes of higher order using the
backward differentiation formulae for an elliptic–parabolic problem, which includes multiple-network poroelasticity
as a special case. These schemes were first introduced in [Altmann, Maier, Unger, BIT Numer. Math., 64:20, 2024],
where a convergence proof for the second-order case is presented. Here, we present a slightly modified version of
these schemes using a different construction of related time delay systems. We present a novel convergence proof
relying on concepts from G-stability applicable for any order and providing a sharper characterization of the required
weak coupling condition. The key tool for the convergence analysis is the construction of a weighted norm enabling
a telescoping argument for the sum of the errors.