delta_moments.h#

#include <sif/structures/delta_moments.h>
SIF_STRUCTURES_DELTA_MOMENTS_H#

Spectral moments of the density contrast, over a set of smoothing radii.

A moment set is one object holding sigma_0 through sigma_order at every radius, rather than one object per order. That is deliberate: the orders are only meaningful together. sigma_0 and sigma_2 describe the same field only if they came from the same radii and the same smoothing window, and every quantity built from them – gamma, R_star, the BBKS densities – reads several orders at once. Bundling them makes a mismatched combination impossible to express.

It costs almost nothing to compute them together, either: the k-sweep evaluates the window once and folds in the k^(2j) weight per order, so each extra order adds a multiply and an accumulate per sample.

If you only need sigma_0, ask for order 0. Both producers take the highest order as a parameter, and a set of order 0 allocates exactly one array. To read one order out of a larger set, use sif_delta_moments_sigma().

SIF_MAX_MOMENT_ORDER#

Highest spectral moment order the estimators accept.

struct sif_delta_moments_t#

Spectral moments sigma_0 .. sigma_order, at several smoothing radii.

sigma_j carries units of length^-j. Produced either by measuring a gridded field (sif_delta_moments_grid()) or by integrating a model power spectrum (sif_delta_moments_pk()); released with sif_delta_moments_free().

uint8_t order#

Highest order computed.

uint8_t n_moments#

order + 1.

sif_real *radii#

The n_radii smoothing radii.

sif_real *sigma#

n_moments * n_radii values, order-major: all radii for j = 0, then all radii for j = 1, and so on. Read it through sif_delta_moments_sigma() rather than indexing by hand.

sif_real *high_k_fraction#

Same layout as #sigma. Fraction of each sum or integral coming from the top half of the available k range: above half Nyquist for the grid estimator, above half of k_max for the P(k) one. A large value means the moment is dominated by the smallest scales the input resolves, and so is set by the resolution rather than by the field.

uint32_t *offsets#

n_moments + 1 entries. offsets[j] is where order j’s block of n_radii values starts in #sigma and #high_k_fraction.

void sif_delta_moments_free(sif_delta_moments_t *moments)#

Release a moment set.

Parameters:

  • moments – Set to free. NULL is accepted and ignored.

const sif_real *sif_delta_moments_sigma(const sif_delta_moments_t *moments, uint8_t order)#

The n_radii values of sigma_order.

Parameters:

  • moments – The moment set.

  • order – Order to read.

Returns:

Borrowed pointer into moments, valid as long as it is and not to be freed. NULL if that order was not computed.