xfem

Documentation

A preliminary collection of documentation (demos, tutorials, mini API) can be found here. A simple doxygen collection of NGSolve, ngsxfem and ngstrefftz C++ API can be found here.

About ngsxfem

ngsxfem is an add-on library to the finite element package Netgen/NGSolve which enables the use of unfitted finite element technologies known as XFEM, CutFEM, TraceFEM, Finite Cell, ... . ngsxfem is an academic software. Its primary intention is to facilitate the development and validation of new numerical methods for partial differential equations.

The features of ngsxfem

The main features of ngsxfem are:

• Tools to work on a subset of the triangulation, the "active mesh" only
• Numerical integration on geometries that are (implicitly) described through level set functions.
• Higher order representation of level set geometries
• Space-Time Finite Elements for the treatment of moving domain problems
• All these features combined with the usual flexibility and power of NGSolve.

ngsxfem has been used in a variety of applications. In the document doc/feature-details.md (see also compiled pdf ) more details on the features is given and in doc/literature.md (see also literature ) an overview of the scientific literature where ngsxfem is used is provided.

Not all features of ngsxfem and NGSolve can directly be combined. Here is an overview of ngsxfem and NGSolve features and if they can directly be combined:

Features ⇲	CFE	XFE	DG	Iso	MLS	ST	Gh	Ag	Hex	Tet	MPI
CFE: CutFEM form.	/	/	y	y	y	y	y	y	y	y	y
XFE: XFEM formulation	/	/	y	y	n	n	y	n	y	y	y
DG: Discont. Galerkin	y	y	/	y	n	y	y	y	y	y	n
Iso: isoparametric map	y	y	y	/	n	y	y	y	y	y	y
MLS: multiple level set	y	n	n	n	/	n	y	y	n	y	y
ST: space-time FEM	y	n	y	y	n	/	y	n	y	y	y
Gh: Ghost penalty	y	y	y	y	y	y	/	/	y	y	n
Ag: Agg. FEM	y	n	y	y	y	n	/	/	y	y	n
Hex: quads / hexes	y	y	y	y	n	y	y	y	/	/	y
Tet: trigs./tets	y	y	y	y	y	y	y	y	/	/	y
MPI: MPI	y	y	n	y	y	y	n	n	y	y	/

Some of the nos are work in progress and some have not been considered so far. If you need a certain combination to work, please contact us and we will see what we can do.

Examples and Documentation

We provide two main sources with which to learn how to use ngsxfem:

• At https://github.com/ngsxfem/ngsxfem-jupyter you can find tutorial-style jupyter notebooks for ngsxfem. These explain the core functionalities and usage of the tools provided by ngsxfem. You can run those tutorials interactively (without the need of a local installation) through binder.
• In the demos-directory we provide several examples that demonstrate the usage of ngsxfem features. See demos/README.md for details.

Installation

We provide installation instructions for building/installing through pip and building/installing from sources in INSTALLATION.md. Further, a docker image is available which can be used to run ngsxfem through docker.

List of contributing authors

Major contributions:

• Christoph Lehrenfeld (main author)
• Fabian Heimann (cut integration, space-time, AggFEM)
• Henry von Wahl (multiple levelsets, mac support, AggFEM)
• Janosch Preuss (space-time)
• Thomas Ludescher (multigrid)
• Paul Stocker (CI, docu, builds, AggFEM)

Additional contributions:

• Pedro Costa Klein (CI, docu)
• Maximilian Zienecker (SIMD, CI)

Community guidelines

If you observe any problems with the software / examples / documentation / installation or want to contribute, you can get in touch with us through either:

• the github issue tracker
• the NGSolve user forum.

Citing

If you use ngsxfem for academic work, please consider citing our publication:

C. Lehrenfeld, F. Heimann, J. Preuß and H. von Wahl
ngsxfem: Add-on to NGSolve for geometrically unfitted finite element discretizations
Journal of Open Source Software, 6(64), 3237,
https://doi.org/10.21105/joss.03237