Configuring SWIFT with VELOCIraptor

In the following three paragraphs we will explain how to setup VELOCIraptor, how to compile it and how to compile SWIFT with VELOCIraptor.

Setting up VELOCIraptor

Before we can run SWIFT with VELOCIraptor we first need to download VELOCIraptor. This can be done by cloning the repository on GitHub:

git clone

The SWIFT interface is in the master branch of VELOCIraptor so nothing is more is needed besides fetching the latest version of the NBodyLib that the code relies upon:

cd VELOCIraptor-STF
git submodule update --init --recursive

To get VELOCIraptor working with SWIFT simply use:

mkdir build
cd build

The first parameter activates the processing of gas, stars and black holes. It can be omitted for simulations evolving only dark matter.

If you wish to run swift without MPI, you will need to add -DVR_MPI=OFF.

Compiling VELOCIraptor

After we downloaded the files and made a configuration file we can compile VELOCIraptor as follows:

make -j

After the compilation of your code, you will find a static library libvelociraptor.a, that is required to run SWIFT with VELOCIraptor. Note that VELOCIraptor needs a serial version of the HDF5 library, not a parallel build.

Compiling SWIFT

The next part is compiling SWIFT with VELOCIraptor and assumes you already downloaded SWIFT from the GitLab repository. This can be done by running

./configure --with-velociraptor=/path/to/VELOCIraptor-STF/build/src

In which ./ only needs to be run once after the code is cloned from the GitLab, and /path/to/ is the path to the VELOCIraptor-STF directory on your machine. Note that this path must be absolute (i.e. relative to /, if you want to run the MPI version of VELOCIraptor as well as a non-MPI one with the same version of SWIFT, then you will need to compile VELOCIraptor twice and create two builds, then use the --with-velociraptor-mpi configure option to point to the MPI build and the --with-velociraptor option to point at the non-MPI build. In general ./configure can be run with other options as desired.

If you see reports about missing references to MPI::Comm and similar functions, then you will also need to include the C++ version of the MPI library in LIBS variable as part of the configuration (or by setting the LIBS environment variable), as in:

./configure --with-velociraptor=/path/to/VELOCIraptor-STF/build/src LIBS=-lmpi++

other names and libraries may be necessary as these are MPI flavour determined.

After this we can run SWIFT with VELOCIraptor, but for this we first need to add several lines to the yaml file of our simulation

  config_file_name:     vrconfig_3dfof_subhalos_SO_hydro.cfg
  basename:             haloes
  scale_factor_first:   0.02
  delta_time:           1.02

In which we specify the .cfg file that is used by VELOCIraptor and the other parameters which SWIFT needs to use. In the case of the Small Cosmological Volume DMO example we can run a simulation with halo finder as:

cd examples/SmallCosmoVolume_DM
../swift --cosmology --hydro --self-gravity --velociraptor --threads=8 small_cosmo_volume_dm.yml

Which activates the VELOCIraptor interface.