running swift and velociraptor

This guide describes how to run SWIFT with the structure finding code called VELOCIraptor and how to run VELOCIraptor stand-alone.

1. Running SWIFT with VELOCIraptor

• Structure finding can be turned on using the flag -x at runtime:

mpirun -np 1 ../swift_mpi -G -t 4 eagle_6.yml -x

• The parameter file now has an extra section called StructureFinding that has options for running with VELOCIraptor
• VELOCIraptor also requires a configuration file of its own. A default configuration file called sample.cfg can be found in the examples/ directory in VELOCIraptor.

Note: To build on CRAY systems you may need to set the following environment variable to enable dynamic linking of libraries:

export CRAYPE_LINK_TYPE=dynamic

2. Running VELOCIraptor stand-alone

• To build VELOCIraptor to run on its own follow Section 2 but set SWIFTINTERACE="off" in the Makefile.config
• Then to run VELOCIraptor you can use the following command:

/path/to/VELOCIraptor/bin/stf-gas -I 2 -i snap_0199 -C stf_input_6dfof_dmonly_sub.cfg -o ./halo/

where -I specifies the snapshot format (Gadget, HDF5, etc.), -i tells it the input file without the file extension, -C specifies the config file to use and -o specifies the base name of the output file.

• A more detailed description of running VELOCIraptor can be found here: https://velociraptor-stf.readthedocs.io/en/latest/

3. Running VELOCIraptor with OpenMP

• VELOCIraptor can be run with OpenMP both stand-alone and from within SWIFT.
• Enable OpenMP compilation in the VELOCIraptor Makefile.config file by setting OMP="on"
• Before running with VELOCIraptor set how many OpenMP threads are required via:

export OMP_NUM_THREADS=28

• You should get the following message when VELOCIraptor runs:

VELOCIraptor/STF running with OpenMP. Number of openmp threads: 28