nbodykit.algorithms.threeptcf¶

Classes

class nbodykit.algorithms.threeptcf.Multipoles3PCF(source, poles, edges, BoxSize=None, periodic=True, weight='Weight', selection='Selection')[source]¶

Compute the multipoles of the isotropic, three-point correlation function in configuration space.

This uses the algorithm of Slepian and Eisenstein, 2015 which scales as \(\mathcal{O}(N^2)\), where \(N\) is the number of objects.

Results are computed when the object is inititalized. See the documenation of run() for the attributes storing the results.

Parameters:

source (CatalogSource) – the input source of particles providing the ‘Position’ column poles (list of int) – the list of multipole numbers to compute edges (array_like) – the edges of the bins of separation to use; length of nbins+1 BoxSize (float, 3-vector, optional) – the size of the box; if periodic boundary conditions used, and ‘BoxSize’ not provided in the source attrs, it must be provided here periodic (bool, optional) – whether to use periodic boundary conditions when computing separations between objects weight (str, optional) – the name of the column in the source specifying the particle weights selection (str, optional) – if not None, the name of the column to use to select certain objects; should be the name of a boolean column

References

Slepian and Eisenstein, MNRAS 454, 4142-4158 (2015)

Methods

load(filename[, comm])	Load a Multipoles3PCF result from filename that has been saved to disk with save().
run()	Compute the three-point CF multipoles.
save(output)	Save the poles result to a JSON file with name output

classmethod load(filename, comm=None)[source]¶

Load a Multipoles3PCF result from filename that has been saved to disk with save().

run()[source]¶

Compute the three-point CF multipoles. This attaches the following the attributes to the class:

• poles

poles¶

BinnedStatistic – a BinnedStatistic object to hold the multipole results; the binned statistics stores the multipoles as variables zeta_0, zeta_1, etc for \(\ell=0,1,\) etc. The coordinates of the binned statistic are r1 and r2, which give the separations between the three objects in CF

save(output)[source]¶

Save the poles result to a JSON file with name output

class nbodykit.algorithms.threeptcf.YlmCache(ells, comm)[source]¶

A class to compute spherical harmonics \(Y_{lm}\) up to a specified maximum \(\ell\)

During calculation, the necessary power of Cartesian unit vectors are cached in memory to avoid repeated calculations for separate harmonics.

Methods

__call__(xpyhat, zhat)

Return a dictionary holding Ylm for each (l,m) combination

__call__(xpyhat, zhat)[source]¶

Return a dictionary holding Ylm for each (l,m) combination required

Parameters:	xpyhat (array_like) – a complex array holding xhat + i * yhat, where xhat and yhat are the two cartesian unit vectors zhat (array_like) – the third cartesian unit vector