.. _converting_ddtheta_mocks:

Calculating the angular correlation function, :math:`\omega(\theta)`
====================================================================

Angular pair counts can be converted into a :math:`\omega(\theta)`
by using the helper function :py:mod:`Corrfunc.utils.convert_3d_counts_to_cf`.
First, we have to compute the relevant pair counts using the python
wrapper :py:mod:`Corrfunc.mocks.DDtheta_mocks`


.. code-block:: python

          >>> from os.path import dirname, abspath, join as pjoin
          >>> import numpy as np
          >>> import Corrfunc
          >>> from Corrfunc.mocks.DDtheta_mocks import DDtheta_mocks
          >>> from Corrfunc.io import read_catalog
          >>> from Corrfunc.utils import convert_3d_counts_to_cf

          >>> galaxy_catalog=pjoin(dirname(abspath(Corrfunc.__file__)),
          ...                     "../mocks/tests/data",
          ...                     "Mr19_mock_northonly.rdcz.ff")
          
          # Read the supplied galaxies on a periodic box
          >>> RA, DEC, _ = read_catalog(galaxy_catalog)

          # Read the supplied randoms catalog
          >>> random_catalog=pjoin(dirname(abspath(Corrfunc.__file__)),
          ...                     "../mocks/tests/data", "Mr19_randoms_northonly.rdcz.ff")
          >>> rand_RA, rand_DEC, _ = read_catalog(random_catalog)
          >>> rand_N = len(rand_RA)

          # Setup the bins
          >>> nbins = 10
          >>> bins = np.linspace(0.1, 10.0, nbins + 1) # note the +1 to nbins

          # Number of threads to use
          >>> nthreads = 2
          
          # Auto pair counts in DD
          >>> autocorr=1
          >>> DD_counts = DDtheta_mocks(autocorr, nthreads, bins,
          ...                          RA, DEC)
          
          # Cross pair counts in DR
          >>> autocorr=0
          >>> DR_counts = DDtheta_mocks(autocorr, nthreads, bins,
          ...                           RA, DEC,
          ...                           RA2=rand_RA, DEC2=rand_DEC)
                         
          # Auto pairs counts in RR
          >>> autocorr=1                         
          >>> RR_counts = DDtheta_mocks(autocorr, nthreads, bins,
          ...                           rand_RA, rand_DEC)

          # All the pair counts are done, get the angular correlation function
          >>> wtheta = convert_3d_counts_to_cf(N, N, rand_N, rand_N,
          ...                                 DD_counts, DR_counts,
          ...                                 DR_counts, RR_counts)

See the complete reference here :py:mod:`Corrfunc`.