Cosmic Web classifier for the IllustrisTNG simulations based on the deformation tensor approach (Hahn et al. 2007, Forero-Romero et al. 2009).

These tools were developed by Davide Martizzi to perform published work in computational astrophysics. Please, reference Martizzi et al. (2019) if you use this code.

Cosmic Web classification is performed with two Python scripts:

• spider_make_mass_grid.py interpolates the mass of the particles in the simulation box into a regular Cartesian grid.
• spider_make_web.py computes the deformation tensor at each node of the Cartesian grid, and performs Cosmic Web classification using the local eigenvalues of the deformation tensor.

The io_utils.py module contains a few functions for I/O and for operations on Cartesian grids; some of this code relies on the h5py package and on Mark Vogelsberger's python-cosmo tools. The I/O functions can be modified to import output from any simulation code.

The scripts are parallelized with mpi4py.

Let us assume that we want to run the scripts on 4 cores.

• Step 1: make a mass grid and print it in hdf5 format:

  mpirun -np 4 python spider_make_mass_grid.py

• Step 2: run the Cosmic Web classifier and print results in hdf5 format:

  mpirun -np 4 python spider_make_web.py 0 4 0.3

  where the command line arguments mean that the script runs at redshift z=0, that the cosmic density field will be smoothed with a filter of radius R = 4 Mpc/h, and that the Cosmic Web classification threshold for the eigenvalues of the deformation tensor is lambda_th=0.3 (see Martizzi et al. 2019 for details).