Llama Multi-Block Infrastructure publicly available


The Llama Multi-Block Infrastructure for Cactus is now publicly available under the GNU General Public License. Llama provides three-dimensional multi-block capability for Cactus-based simulations that can be combined with Carpet’s adaptive mesh refinement functionality. Llama decomposes the domain into multiple (potentially overlapping) blocks with different local coordinate systems. This allows e.g. spherical domains, spherical excision, adaptive radial/angular resolution, etc., without incurring coordinate singularities.

Llama provides several patch systems suitable for single and binary objects in relativistic astrophysics, and is well integrated with the Einstein Toolkit . Llama was already used for several publications , and we believe the code is ready to be used in other projects. We are seeking volunteers to help us add tutorials and documentation, improve error messages, and generally shake down and brush up the code for a future inclusion in the Einstein Toolkit.

To aid others in getting started using Llama, we will be hosting a virtual workshop where we provide an overview of the code and answer questions. Details will be announced shortly.

Llama constitutes the fruit of a significant effort of several people over several years. We make Llama public to help modernize the computational tools used in our community, and in the hope to boost Llama itself by inviting contributions from everybody. We ask you to acknowledge our effort by following the citation guidelines described on .

The Llama groomers:

R. Haas, I. Hinder, D. Pollney, C. Reisswig, E. Schnetter, B. Wardell

Llama Multi-Block Infrastructure

The Llama code is a 3-dimensional multiblock infrastructure with adaptive mesh-refinement for Cactus based on Carpet. It provides different patch systems that cover the simulation domain by a set of overlapping patches. Each of these patches has local cooordinates with a well-defined relation to global Cartesian coordinates. However, all computations are carried out using a global Cartesian tensor basis such that complicated tensor transformations between patch systems can be avoided. Information between the different patches is communicated via interpolation in the overlap zones.

The main field of application is currently numerical relativity, and especially the full non-linear 3-dimensional evolution of binary black hole mergers, stellar core-collapse and computation of the associated gravitational-wave signatures.

With topologically spherical grids in the wave-zone, it is possible to resolve the gravitational waves with high accuracy, while at the same time employing Cartesian adaptive mesh refinement grids around the black holes to provide a well established discretized representation of the strong field region.