# Higher-order linearly implicit full discretization of the Landau--Lifshitz--Gilbert equation

## TL;DR

This paper develops and analyzes higher-order linearly implicit BDF time discretizations combined with advanced finite element methods for the Landau--Lifshitz--Gilbert equation, proving stability and error bounds.

## Contribution

It introduces a novel combination of BDF methods up to order 5 with non-conforming finite element discretizations for LLG, providing rigorous stability and error analysis.

## Key findings

- Stable and optimal error bounds for BDF methods of orders 3 to 5.
- No time step restriction needed for BDF orders 1 and 2.
- Discrete energy inequality established for certain methods.

## Abstract

For the Landau--Lifshitz--Gilbert (LLG) equation of micromagnetics we study linearly implicit backward difference formula (BDF) time discretizations up to order $5$ combined with higher-order non-conforming finite element space discretizations, which are based on the weak formulation due to Alouges but use approximate tangent spaces that are defined by $L^2$-averaged instead of nodal orthogonality constraints. We prove stability and optimal-order error bounds in the situation of a sufficiently regular solution. For the BDF methods of orders $3$ to~$5$, this requires %a mild time step restriction $\tau \leqslant ch$ and that the damping parameter in the LLG equations be above a positive threshold; this condition is not needed for the A-stable methods of orders $1$ and $2$, for which furthermore a discrete energy inequality irrespective of solution regularity is proved.