# nbodykit.source.mesh.species¶

Classes

 MultipleSpeciesCatalogMesh(source, Nmesh, …) A subclass of CatalogMesh designed to paint the density field from a sum of multiple types of particles.
class nbodykit.source.mesh.species.MultipleSpeciesCatalogMesh(source, Nmesh, BoxSize, dtype, selection, position, weight, value, interlaced, compensated, resampler)[source]

A subclass of CatalogMesh designed to paint the density field from a sum of multiple types of particles.

The compute() function paints the density field summed over all particle species.

Parameters
• source (CatalogSource) – the input catalog that we wish to interpolate to a mesh

• BoxSize – the size of the box

• Nmesh (int, 3-vector) – the number of cells per mesh side

• dtype (str) – the data type of the values stored on mesh

• weight (str) – column in source that specifies the weight value for each particle in the source to use when gridding

• value (str) – column in source that specifies the field value for each particle; the mesh stores a weighted average of this column

• selection (str) – column in source that selects the subset of particles to grid

• position (str, optional) – column in source specifying the position coordinates; default is Position

Attributes
actions

The actions to apply to the interpolated density field, optionally included the compensation correction.

attrs

A dictionary storing relevant meta-data about the CatalogSource.

compensated

Boolean flag to indicate whether to correct for the windowing kernel introduced when interpolating the discrete particles to a continuous field.

interlaced

Whether to use interlacing when interpolating the density field.

resampler

String specifying the name of the interpolation kernel when gridding the density field.

window

Methods

 apply(self, func[, kind, mode]) Return a view of the mesh, with actions updated to apply the specified function, either in Fourier space or configuration space, based on mode compute(self[, mode, Nmesh]) Compute / Fetch the mesh object into memory as a RealField or ComplexField object. preview(self[, axes, Nmesh, root]) Gather the mesh into as a numpy array, with (reduced) resolution. save(self, output[, dataset, mode]) Save the mesh as a BigFileMesh on disk, either in real or complex space. to_complex_field(self[, out]) Convert the mesh source to the Fourier-space field, returning a pmesh.pm.ComplexField object. to_field(self[, mode, out]) Return the mesh as a pmesh Field object, either in Fourier space or configuration space, based on mode. to_real_field(self[, normalize]) Paint the density field holding the sum of all particle species, returning a RealField object. view(self) Return a “view” of the MeshSource, in the spirit of numpy’s ndarray view.
 paint
__finalize__(self, other)

Finalize the creation of a MeshSource object by copying over attributes from a second MeshSource.

Parameters

other (MeshSource) – the second MeshSource to copy over attributes from

__getitem__(self, key)[source]

If indexed by a species name, return a CatalogMesh object holding only the data columns for that species with the same parameters as the current object.

If not a species name, this has the same behavior as CatalogSource.__getitem__().

__len__(self)

Length of a mesh source is zero

actions

The actions to apply to the interpolated density field, optionally included the compensation correction.

apply(self, func, kind='wavenumber', mode='complex')

Return a view of the mesh, with actions updated to apply the specified function, either in Fourier space or configuration space, based on mode

Parameters
• func (callable or a MeshFilter object) – func(x, y) where x is a list of r (k) values that broadcasts into a full array, when mode is ‘real’ (‘complex’); the value of x depends on kind. y is the value of the mesh field on the corresponding locations.

• kind (string, optional) –

if a MeshFilter object is given as func, this is ignored. The kind of value in x.

• When mode is ‘complex’:

• ’wavenumber’ means wavenumber from [- 2 pi / L * N / 2, 2 pi / L * N / 2).

• ’circular’ means circular frequency from [- pi, pi).

• ’index’ means [0, Nmesh )

• When mode is ‘real’:

• ’relative’ means distance from [-0.5 Boxsize, 0.5 BoxSize).

• ’index’ means [0, Nmesh )

• mode ('complex' or 'real', optional) – if a MeshFilter object is given as func, this is ignored. whether to apply the function to the mesh in configuration space or Fourier space

Returns

a view of the mesh object with the actions attribute updated to include the new action

Return type

MeshSource

attrs

A dictionary storing relevant meta-data about the CatalogSource.

compensated

Boolean flag to indicate whether to correct for the windowing kernel introduced when interpolating the discrete particles to a continuous field.

See the documentation for further details.

compute(self, mode='real', Nmesh=None)

Compute / Fetch the mesh object into memory as a RealField or ComplexField object.

interlaced

Whether to use interlacing when interpolating the density field. See the documentation for further details.

preview(self, axes=None, Nmesh=None, root=0)

Gather the mesh into as a numpy array, with (reduced) resolution. The result is broadcast to all ranks, so this uses $$\mathrm{Nmesh}^3$$ per rank.

Parameters
• Nmesh (int, array_like) – The desired Nmesh of the result. Be aware this function allocates memory to hold a full Nmesh on each rank.

• axes (int, array_like) – The axes to project the preview onto., e.g. (0, 1)

• root (int, optional) – the rank number to treat as root when gathering to a single rank

Returns

out – An numpy array holding the real density field.

Return type

array_like

resampler

String specifying the name of the interpolation kernel when gridding the density field.

See the documentation for further details.

Note

Valid values must be in pmesh.resampler.methods

save(self, output, dataset='Field', mode='real')

Save the mesh as a BigFileMesh on disk, either in real or complex space.

Parameters
• output (str) – name of the bigfile file

• dataset (str, optional) – name of the bigfile data set where the field is stored

• mode (str, optional) – real or complex; the form of the field to store

to_complex_field(self, out=None)

Convert the mesh source to the Fourier-space field, returning a pmesh.pm.ComplexField object.

Not implemented in the base class, unless object is a view.

to_field(self, mode='real', out=None)

Return the mesh as a pmesh Field object, either in Fourier space or configuration space, based on mode.

This will call to_real_field() or to_complex_field() based on mode.

Parameters

mode ('real' or 'complex') – the return type of the field

Returns

either a RealField of ComplexField, storing the value of the field on the mesh

Return type

RealField, ComplexField

to_real_field(self, normalize=True)[source]

Paint the density field holding the sum of all particle species, returning a RealField object.

Meta-data computed for each particle is stored in the attrs attribute of the returned RealField, with keys that are prefixed by the species name. In particular, the total shot noise for the mesh is defined as:

$P_\mathrm{shot} = \sum_i (W_i/W_\mathrm{tot})^2 P_{\mathrm{shot},i},$

where the sum is over all species in the catalog, W_i is the sum of the Weight column for the $$i^\mathrm{th}$$ species, and $$W_\mathrm{tot}$$ is the sum of $$W_i$$ across all species.

Parameters

normalize (bool, optional) – if True, normalize the density field as $$1+\delta$$, dividing by the total mean number of objects per cell, as given by the num_per_cell meta-data value in attrs

Returns

the RealField holding the painted density field, with a attrs dictionary attribute holding the meta-data

Return type

RealField

view(self)

Return a “view” of the MeshSource, in the spirit of numpy’s ndarray view.

This returns a new MeshSource whose memory is owned by self.

Note that for CatalogMesh objects, this is overidden by the CatalogSource.view function.