[Users] Multigrid elliptic solver released.

[Eloisa Bentivegna]

Dear Cactus and Einstein Toolkit users,

I have been working on a solver for elliptic PDEs based on the multigrid paradigm, and developed as a Cactus thorn using Carpet. The solver is now able to tackle some basic problems and could be applied to other cases of interest to this community. You can obtain a copy by checking out the Cosmology arrangement from its repository:

git clone git at bitbucket.org:eloisa/cosmology.git

There you will also find documentation, license information, and a test suite. There is no tutorial, but I think that what is under docs/ and par/ should suffice to get most people started. For more information, you can also peruse <http://arxiv.org/abs/arXiv:1305.5576>, especially if you are interested in elliptic problems on spaces without boundaries.

Please notice that the spirit of the solver is not to replace existing state-of-the-art tools, but to provide a way of solving elliptic PDEs with is both easy to learn and to extend, and gives reasonable answers in a reasonable amount of time. In order to keep this flexibility, the solver is simply unable to compete with other software tailored to specific equations or geometries. In areas where these alternatives exist, they should be used instead.

Finally, beware of the lack of explicit support for some of the latest Carpet features, such as multipatch and cell-centered grids. Being unfamiliar with these features, I cannot estimate how much work would be necessary to include them. 

I hope many of you will find this tool useful, and I look forward to hear your feedback.

Eloisa