API Reference

The full list of nbodykit modules is available here. We summarize the most important aspects of the API below.

The IO Library (nbodykit.io)

Base class:

FileType An abstract base class representing a file object.

Subclasses available from the nbodykit.io module:

BigFile(path[, exclude, header, dataset]) A file object to handle the reading of columns of data from a bigfile file.
BinaryFile(path, dtype[, offsets, …]) A file object to handle the reading of columns of data from a binary file.
CSVFile(path, names[, blocksize, dtype, …]) A file object to handle the reading of columns of data from a CSV file.
FITSFile(path[, ext]) A file object to handle the reading of FITS data using the fitsio package.
HDFFile(path[, root, exclude]) A file object to handle the reading of columns of data from a h5py HDF5 file.
FileStack(filetype, path, *args, **kwargs) A file object that offers a continuous view of a stack of subclasses of FileType instances.
TPMBinaryFile(path[, precision]) Read snapshot binary files from Martin White’s TPM simulations.

Cosmology (nbodykit.cosmology)

Cosmology([H0, Om0, Ob0, Ode0, w0, Tcmb0, …]) An extension of the astropy.cosmology framework that can store additional, orthogonal parameters and behaves like a read-only dictionary.
EHPower(cosmo, redshift) Linear power spectrum using the Eisenstein & Hu (1998) fitting formula with BAO wiggles.
NoWiggleEHPower(cosmo, redshift) Linear power spectrum using the Eisenstein & Hu (1998) fitting formula without BAO wiggles.
PerturbationGrowth(cosmo[, a]) Perturbation Growth coefficients at several orders.

Built-in cosmologies:

Name Source H0 Om Flat
WMAP5 Komatsu et al. 2009 70.2 0.277 Yes
WMAP7 Komatsu et al. 2011 70.4 0.272 Yes
WMAP9 Hinshaw et al. 2013 69.3 0.287 Yes
Planck13 Planck Collab 2013, Paper XVI 67.8 0.307 Yes
Planck15 Planck Collab 2015, Paper XIII 67.7 0.307 Yes

Transforming Catalog Data (nbodykit.transform)

ConcatenateSources(*sources, **kwargs) Concatenate CatalogSource objects together, optionally including only certain columns in the returned source.
StackColumns(*cols) Stack the input dask arrays vertically, column by column.
ConstantArray(value, size[, chunks]) Return a dask array of the specified size holding a single value.
SkyToUnitSphere(ra, dec[, degrees]) Convert sky coordinates (ra, dec) to Cartesian coordinates on the unit sphere.
SkyToCartesion(ra, dec, redshift, cosmo[, …]) Convert sky coordinates (ra, dec, redshift) to a Cartesian Position column.
HaloConcentration(mass, cosmo, redshift[, mdef]) Return halo concentration from halo mass, based on the analytic fitting formulas presented in Dutton and Maccio 2014.
HaloRadius(mass, cosmo, redshift[, mdef]) Return halo radius from halo mass, based on the specified mass definition.

Data Sources

Discrete Objects

Base class:

CatalogSource(comm[, use_cache]) An abstract base class representing a catalog of discrete particles.

And subclasses:

CSVCatalog(*args, **kwargs) A CatalogSource that uses CSVFile to read data from disk.
BinaryCatalog(*args, **kwargs) A CatalogSource that uses BinaryFile to read data from disk.
BigFileCatalog(*args, **kwargs) A CatalogSource that uses BigFile to read data from disk.
TPMBinaryCatalog(*args, **kwargs) A CatalogSource that uses TPMBinaryFile to read data from disk.
HDFCatalog(*args, **kwargs) A CatalogSource that uses HDFFile to read data from disk.
FITSCatalog(*args, **kwargs) A CatalogSource that uses FITSFile to read data from disk.
ArrayCatalog(data[, comm, use_cache]) A CatalogSource initialized from a dictionary or structured ndarray.
HaloCatalog(source, cosmo, redshift[, mdef, …]) A wrapper CatalogSource of halo objects to interface nicely with halotools.sim_manager.UserSuppliedHaloCatalog.
HODCatalog(halos[, logMmin, sigma_logM, …]) A CatalogSource that uses the HOD prescription of Zheng et al 2007 to populate an input halo catalog with galaxies.
LogNormalCatalog(Plin, nbar, BoxSize, Nmesh) A CatalogSource containing biased particles that have been Poisson-sampled from a log-normal density field.
UniformCatalog(nbar, BoxSize[, seed, comm, …]) A CatalogSource that has uniformly-distributed Position and Velocity columns.
RandomCatalog(csize[, seed, comm, use_cache]) A CatalogSource that can have columns added via a collective random number generator.
FKPCatalog(data, randoms[, BoxSize, BoxPad, …]) An interface for simultaneous modeling of a data CatalogSource and a randoms CatalogSource, in the spirit of Feldman, Kaiser, and Peacock, 1994.
MultipleSpeciesCatalog(names, *species, **kwargs) A CatalogSource interface for handling multiples species of particles.

Interpolating Objects to a Mesh

The base class:

CatalogMesh(source, BoxSize, Nmesh, dtype, …) A class to convert a CatalogSource to a MeshSource, by interpolating the position of the discrete particles on to a mesh.

And subclasses:

MultipleSpeciesCatalogMesh(source, BoxSize, …) A subclass of CatalogMesh designed to paint the density field from a sum of multiple types of particles.
FKPCatalogMesh(source, BoxSize, Nmesh, …) A subclass of MultipleSpeciesCatalogMesh designed to paint a FKPCatalog to a mesh.

Data Directly on a Mesh

Base class:

MeshSource(comm, Nmesh, BoxSize, dtype) Base class for a source in the form of data on an input grid.

And subclasses:

BigFileMesh(path, dataset[, comm]) A MeshSource object that reads a mesh from disk using bigfile.
LinearMesh(Plin, BoxSize, Nmesh[, seed, …]) A MeshSource object that generates a RealField density mesh from a linear power spectrum function \(P(k)\).
FieldMesh(field) A MeshSource initialized from an in-memory Field object, either a pmesh.pm.RealField or pmesh.pm.ComplexField.
ArrayMesh(array, BoxSize[, comm, root]) A MeshSource initalized from an in-memory numpy array.

Algorithms (nbodykit.algorithms)

Clustering Statistics

FFTPower(first, mode[, Nmesh, BoxSize, …]) Algorithm to compute the 1d or 2d power spectrum and/or multipoles in a periodic box, using a Fast Fourier Transform (FFT).
ProjectedFFTPower(first[, Nmesh, BoxSize, …]) The power spectrum of a field in a periodic box, projected over certain axes.
ConvolvedFFTPower(source, poles[, Nmesh, …]) Algorithm to compute power spectrum multipoles using FFTs for a data survey with non-trivial geometry.
Multipoles3PCF(source, poles, edges[, …]) Compute the multipoles of the isotropic, three-point correlation function in configuration space.
SimulationBoxPairCount(mode, source1, redges) Count (weighted) pairs of objects in a simulation box using the Corrfunc package.
SurveyDataPairCount(mode, source1, redges, cosmo) Count (weighted) pairs of objects from a survey data catalog using the Corrfunc package.

Grouping Methods

FOF(source, linking_length, nmin[, absolute]) A friends-of-friends halo finder that computes the label for each particle, denoting which halo it belongs to.
CylindricalGroups(source, rankby, rperp, rpar) Compute groups of objects using a cylindrical grouping method.
FiberCollisions(ra, dec[, collision_radius, …]) Run an angular FOF algorithm to determine fiber collision groups from an input catalog, and then assign fibers such that the maximum amount of object receive a fiber.


KDDensity(source[, margin]) Estimate a proxy density based on the distance to the nearest neighbor.
RedshiftHistogram(source, fsky, cosmo[, …]) Compute the mean number density as a function of redshift \(n(z)\) from an input CatalogSource of particles.

Managing Multiple Tasks (TaskManager)

TaskManager(cpus_per_task[, comm, debug, …]) An MPI task manager that distributes tasks over a set of MPI processes, using a specified number of independent workers to compute each task.
TaskManager.iterate(tasks) A generator that iterates through a series of tasks in parallel.
TaskManager.map(function, tasks) Like the built-in map() function, apply a function to all of the values in a list and return the list of results.

Analyzing Results (BinnedStatistic)

BinnedStatistic(dims, edges, data[, …]) Lightweight class to hold statistics binned at fixed coordinates.
BinnedStatistic.from_json(filename[, key, …]) Initialize a BinnedStatistic from a JSON file.
BinnedStatistic.to_json(filename) Write a BinnedStatistic from a JSON file.
BinnedStatistic.copy() Returns a copy of the BinnedStatistic
BinnedStatistic.rename_variable(old_name, …) Rename a variable in data from old_name to new_name.
BinnedStatistic.average(dim, **kwargs) Compute the average of each variable over the specified dimension.
BinnedStatistic.reindex(dim, spacing[, …]) Reindex the dimension dim by averaging over multiple coordinate bins, optionally weighting by weights.
BinnedStatistic.sel([method]) Return a new BinnedStatistic indexed by coordinate values along the specified dimension(s).
BinnedStatistic.squeeze([dim]) Squeeze the BinnedStatistic along the specified dimension, which removes that dimension from the BinnedStatistic.

Internal Nuts and Bolts

MPI Utilities

nbodykit.CurrentMPIComm A class to faciliate getting and setting the current MPI communicator.
nbodykit.CurrentMPIComm.enable(func) Decorator to attach the current MPI communicator to the input keyword arguments of func, via the comm keyword.
nbodykit.CurrentMPIComm.get() Get the current MPI communicator, returning MPI.COMM_WORLD if it has not be explicitly set yet.
nbodykit.CurrentMPIComm.set(comm) Set the current MPI communicator to the input value.
nbodykit.utils.GatherArray(data, comm[, root]) Gather the input data array from all ranks to the specified root.
nbodykit.utils.ScatterArray(data, comm[, …]) Scatter the input data array across all ranks, assuming data is initially only on root (and None on other ranks).

General Utilities

nbodykit.setup_logging([log_level]) Turn on logging, with the specified level.
nbodykit.utils.JSONEncoder([skipkeys, …]) A subclass of json.JSONEncoder that can also handle numpy arrays, complex values, and astropy.units.Quantity objects.
nbodykit.utils.JSONDecoder(*args, **kwargs) A subclass of json.JSONDecoder that can also handle numpy arrays, complex values, and astropy.units.Quantity objects.

Generating Mock Data

nbodykit.mockmaker.gaussian_complex_fields(pm, …) Make a Gaussian realization of a overdensity field, \(\delta(x)\).
nbodykit.mockmaker.gaussian_real_fields(pm, …) Make a Gaussian realization of a overdensity field in real-space \(\delta(x)\).
nbodykit.mockmaker.poisson_sample_to_points(…) Poisson sample the linear delta and displacement fields to points.