spherical_finder.h#

#include <sif/finder/spherical_finder.h>
SIF_FINDER_SPHERICAL_FINDER_H#

Spherical void finder: fixed-radius spheres on a density grid.

Walks the smoothing radii from largest to smallest. At each radius it collects every grid cell at or below the threshold, visits them deepest first, and accepts a sphere of exactly that radius wherever one does not overlap a void already accepted. Cells swallowed by an accepted void are masked, so later and smaller radii cannot re-find the same underdensity.

Voids therefore come out with radii drawn from the ladder that was passed in, not from the data. sif_finder_exodus() relaxes that by growing each sphere to the radius the tracers actually support.

sif_catalog_t *sif_finder_spherical(sif_grid_t *grid, const sif_real *radii, uint32_t n_radii, sif_real threshold, sif_real overlap_fraction, sif_option opt)#

Run the spherical void finder on a density grid.

Parameters:

  • grid – Density contrast field, as produced by sif_grid_to_density_contrast(). The finder smooths it in place at each radius and transforms the original back at the end, so on return it holds what it held on entry. Pass SIF_FINDER_CONSUME_GRID to skip that final transform.

  • radii – Smoothing radii to try. Order does not matter: the finder sorts them descending, since accepting the large voids first is what makes the mask meaningful.

  • n_radii – Number of radii.

  • threshold – Density contrast a cell must be at or below to seed a void. Negative, since voids are underdensities.

  • overlap_fraction – How much two voids may overlap, as a fraction of the smaller one’s radius: they collide when their separation falls below r1 + r2 - overlap_fraction * min(r1, r2). 0 forbids overlap entirely; 1 lets the smaller void’s radius be swallowed.

  • opt – Finder options. Honours SIF_FINDER_CONSUME_GRID and SIF_FINDER_KEEP_CIC_WINDOW. The box is always periodic.

Note

The grid is assumed to have been built by sif_grid_assign_cic(), whose window is divided back out before the first smoothing so that the top-hat is the only window applied. Pass SIF_FINDER_KEEP_CIC_WINDOW for a grid that was filled some other way.

Returns:

Newly allocated catalogue, released with sif_catalog_free(), or NULL on invalid input or failure.

Warning

grid->values is reassigned during the run: the original buffer is released once its contents are in the FFT workspace, and the workspace’s is handed back at the end. The contents are restored, the pointer is not, so a pointer cached from before the call dangles afterwards.