delta_moments.h#

#include <sif/measure/delta_moments.h>
SIF_MEASURE_DELTA_MOMENTS_H#

Measuring the spectral moments of a gridded density field.

The counterpart to sif_delta_moments_pk(), which evaluates the same moments from a model spectrum: measuring one field and modelling another is how a measurement is checked against theory, so the two deliberately produce the same container.

sif_delta_moments_t *sif_delta_moments_grid(const sif_grid_t *grid, const sif_real *radii, uint32_t n_radii, uint8_t order, uint64_t n_tracers, uint64_t seed, sif_option opt)#

Measure the spectral moments of a gridded density field.

Parameters:

  • grid – Density contrast field, from sif_grid_to_density_contrast(). Read only.

  • radii – Smoothing radii, each at least two cell lengths and at most half the box; see sif_delta_distribution_grid() on why smaller is rejected.

  • n_radii – Number of radii.

  • order – Highest moment order, at most #SIF_MAX_MOMENT_ORDER. Each extra order costs a multiply and an accumulate per k sample, so ask for what you need and no less: pass 0 if only sigma_0 is wanted.

  • n_tracers – Tracer count behind the grid, used to subtract the shot noise. Pass 0 to leave it in. Assumes unweighted tracers.

  • seed – Seed for the phase shuffle; unused when not shuffling. Shared with sif_delta_distribution_grid() – see there.

  • opt – SIF_DELTA_SHUFFLE_*, SIF_DELTA_FILTER_*, SIF_DELTA_KEEP_CIC_WINDOW.

Returns:

Newly allocated moment set, released with sif_delta_moments_free(), or NULL on invalid input or failure.