Comments (3)
On the plane back from Madrid, I realized that these estimators are actually just the normal xi+ and xi- for the cross correlation between the halo ellipticities and the sources, where the halo ellipticity is normalized to have |g| = 1 (i.e., it is just the phase g1 + i g2 = exp(i phi)).
I made a unit test to confirm this, which is now in the code here (on master, but it works with the current v3.2.1 release -- no extra source code required).
The basic code flow is along the lines of the following:
lens_absg = numpy.sqrt(lens_g1**2 + lens_g2**2)
lens_cat = treecorr.Catalog(ra=lens_ra, dec=lens_dec, g1=lens_g1/lens_absg, g2=lens_g2/lens_absg)
source_cat = treecorr.Catalog(ra=source_ra, dec=source_dec, g1=source_g1, g2=source_g2, w=source_w)
gg = treecorr.GGCorrelation(min_sep=1, max_sep=30, bin_size=0.1)
gg.process(lens_cat, source_cat)
gamma_4theta = gg.xim
gamma_const = gg.xip
gamma_4theta_x = gg.xim_im
gamma_const_x = gg.xip_im
The test I linked to doesn't actually use weights, but those are already implemented. And it uses x,y, just because it is easier to construct the test in Euclidean coordinates. But ra, dec would normally be used on real data.
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So, given the above, do you think there should be a helper function in TreeCorr for this? It's pretty straightforward, despite being non-obvious, so I'm not sure how helpful a helper function would actually be.
Perhaps just some additional documentation to point this out? Maybe in the GGCorrelation class doc string.
Or maybe just in your paper about this, you lay out the math to prove this point, in which case it would be clear to other people making this measurement what functions in TreeCorr to use.
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I think there is nothing further to do on this issue. Closing now.
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Related Issues (20)
- Avoiding repeated writing of identical patches with save_patch_dir HOT 1
- MPI Crash when many patches empty HOT 8
- Computing NN correlation from simulated catalogues without a random catalogue HOT 5
- NNCorrelation error under MPI in 4.2.0 HOT 2
- Bug when using patches and the Rlens metric HOT 2
- Access correlation function for jackknife HOT 2
- multiply-occurring objects bias results low HOT 4
- Installing error on windows HOT 17
- Measuring the correlation function xi by patches HOT 4
- Problem with NN_correlation when setting low_mem=True HOT 1
- NG doesn't work as expected in simulation box with x, y, z HOT 7
- Computing "scaled counts-in-spheres" HOT 4
- TwoD Binning in Rperp metric. HOT 2
- Feature request: create Catalog using derived quantities HOT 3
- possible weight issue for 2pt correlation with cartesian coordinates HOT 2
- bin_slop definition and implementation HOT 7
- Let varg, vark be specifiable by the user, rather than computed
- Outlier point in NN Correlation HOT 3
- is bin_slop in log or linear space when using log binning? HOT 3
- write_patch_results HOT 3
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