Extracting patch IDs from NN_correlation function to perform Alcock–Paczyński test

[stankortmann]

Currently I am using the NNcorrelation class to calculate the D_a(z_eff) inside a hydrodynamical simulation. I did this by using the 2D ra,dec inputs to retrieve the angular seperations and consequently construct the w(theta). On top of that I also want to construct the LOS correlation function to ultimately perform the Alcock–Paczyński test. This is a 1D problem, so in essence it is quite trivial to do outside of the treecorr environment. However, the environment is very efficient and most of all handy when it comes to performing statistical analysis of the correlation function.

Ultimately, I would like to use the patch IDs for all the galaxies inside the w(theta) construction to be able to perform my own analysis of the LOS correlation. Is there any way I can access them within the current framework?

[rmjarvis]

I'm not sure I understand exactly what you need. But maybe this does at least part of what you want:

https://rmjarvis.github.io/TreeCorr/_build/html/correlation2.html#treecorr.Corr2.sample_pairs

That can give you a sample of galaxy pairs that fall into any particular bin in the w(theta) correlation. You can choose the number to be large enough that the "sample" is actually all the pairs if you have enough memory for that.

[stankortmann]

Sorry, my question might have been worded a bit vaguely. In simpler terms: Is there a way to retrieve the patch IDs of all the datapoints whenever I catalogue them with treecorr.Catalog? I.e. I want to know which galaxies are put in a certain patch used in the jackknife method.

[rmjarvis]

Oh, sure. cat.patch is an array of all the patch numbers.