Source code for treecorr.nqcorrelation

# Copyright (c) 2003-2024 by Mike Jarvis
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"""
.. module:: ngcorrelation
"""

import numpy as np

from . import _treecorr
from .catalog import calculateVarQ
from .nzcorrelation import BaseNZCorrelation


[docs]class NQCorrelation(BaseNZCorrelation): r"""This class handles the calculation and storage of a 2-point count-quatrefoil correlation function, where a quatrefoil is any field with spin-4 rotational properties. See the doc string of `Corr3` for a description of how the triangles are binned along with the attributes related to the different binning options. In addition to the attributes common to all `Corr2` subclasses, objects of this class hold the following attributes: Attributes: xi: The correlation function, :math:`\xi(r) = \langle q_R\rangle`. xi_im: The imaginary part of :math:`\xi(r)`. varxi: An estimate of the variance of :math:`\xi` cov: An estimate of the full covariance matrix. raw_xi: The raw value of xi, uncorrected by an RQ calculation. cf. `calculateXi` raw_xi_im: The raw value of xi_im, uncorrected by an RQ calculation. cf. `calculateXi` raw_varxi: The raw value of varxi, uncorrected by an RQ calculation. cf. `calculateXi` .. note:: The default method for estimating the variance and covariance attributes (``varxi``, and ``cov``) is 'shot', which only includes the shape noise propagated into the final correlation. This does not include sample variance, so it is always an underestimate of the actual variance. To get better estimates, you need to set ``var_method`` to something else and use patches in the input catalog(s). cf. `Covariance Estimates`. The typical usage pattern is as follows: >>> nq = treecorr.NQCorrelation(config) >>> nq.process(cat1,cat2) # Compute the cross-correlation. >>> nq.write(file_name) # Write out to a file. >>> xi = nq.xi # Or access the correlation function directly. Parameters: config (dict): A configuration dict that can be used to pass in kwargs if desired. This dict is allowed to have addition entries besides those listed in `Corr2`, which are ignored here. (default: None) logger: If desired, a logger object for logging. (default: None, in which case one will be built according to the config dict's verbose level.) Keyword Arguments: **kwargs: See the documentation for `Corr2` for the list of allowed keyword arguments, which may be passed either directly or in the config dict. """ _cls = 'NQCorrelation' _letter1 = 'N' _letter2 = 'Q' _letters = 'NQ' _builder = _treecorr.NQCorr _calculateVar1 = lambda *args, **kwargs: None _calculateVar2 = staticmethod(calculateVarQ) _zreal = 'qR' _zimag = 'qR_im'
[docs] def finalize(self, varq): """Finalize the calculation of the correlation function. The `Corr2.process_cross` command accumulates values in each bin, so it can be called multiple times if appropriate. Afterwards, this command finishes the calculation by dividing each column by the total weight. Parameters: varq (float): The variance per component of the quatrefoil field. """ super().finalize(varq)
[docs] def calculateXi(self, *, rq=None): r"""Calculate the correlation function possibly given another correlation function that uses random points for the foreground objects. - If rq is None, the simple correlation function :math:`\langle q_R\rangle` is returned. - If rq is not None, then a compensated calculation is done: :math:`\langle q_R\rangle = (DQ - RQ)`, where DQ represents the mean radial quatrefoil field around the data points and RQ represents the mean radial quatrefoil field around random points. After calling this function, the attributes ``xi``, ``xi_im``, ``varxi``, and ``cov`` will correspond to the compensated values (if rq is provided). The raw, uncompensated values are available as ``rawxi``, ``raw_xi_im``, and ``raw_varxi``. Parameters: rq (NQCorrelation): The cross-correlation using random locations as the lenses (RQ), if desired. (default: None) Returns: Tuple containing - xi = array of the real part of :math:`\xi(R)` - xi_im = array of the imaginary part of :math:`\xi(R)` - varxi = array of the variance estimates of the above values """ return super().calculateXi(rz=rq)
[docs] def write(self, file_name, *, rq=None, file_type=None, precision=None, write_patch_results=False, write_cov=False): r"""Write the correlation function to the file, file_name. - If rq is None, the simple correlation function :math:`\langle q_R\rangle` is used. - If rq is not None, then a compensated calculation is done: :math:`\langle q_R\rangle = (DQ - RQ)`, where DQ represents the mean quatrefoil field. around the data points and RQ represents the mean quatrefoil field around random points. The output file will include the following columns: ========== ============================================================= Column Description ========== ============================================================= r_nom The nominal center of the bin in r meanr The mean value :math:`\langle r \rangle` of pairs that fell into each bin meanlogr The mean value :math:`\langle \log(r) \rangle` of pairs that fell into each bin qR The mean real part of the quatrefoil field relative to the center points qR_im The mean imaginary part of the quatrefoil field relative to the center points sigma The sqrt of the variance estimate of either of these weight The total weight contributing to each bin npairs The total number of pairs in each bin ========== ============================================================= If ``sep_units`` was given at construction, then the distances will all be in these units. Otherwise, they will be in either the same units as x,y,z (for flat or 3d coordinates) or radians (for spherical coordinates). Parameters: file_name (str): The name of the file to write to. rq (NQCorrelation): The cross-correlation using random locations as the lenses (RQ), if desired. (default: None) file_type (str): The type of file to write ('ASCII' or 'FITS'). (default: determine the type automatically from the extension of file_name.) precision (int): For ASCII output catalogs, the desired precision. (default: 4; this value can also be given in the constructor in the config dict.) write_patch_results (bool): Whether to write the patch-based results as well. (default: False) write_cov (bool): Whether to write the covariance matrix as well. (default: False) """ super().write(file_name, rq, file_type, precision, write_patch_results, write_cov)