Python module for computing 2-point and 3-point correlation functions
Project description
TreeCorr is a package for efficiently computing 2-point and 3-point correlation functions.
The code is hosted at https://github.com/rmjarvis/TreeCorr
It can compute correlations of regular number counts, weak lensing shears, or scalar quantities such as convergence or CMB temperature fluctutations.
2-point correlations may be auto-correlations or cross-correlations. This includes shear-shear, count-shear, count-count, kappa-kappa, etc. (Any combination of shear, kappa, and counts.)
3-point correlations currently can only be auto-correlations. This includes shear-shear-shear, count-count-count, and kappa-kappa-kappa. The cross varieties are planned to be added in the near future.
Both 2- and 3-point functions can be done with the correct curved-sky calculation using RA, Dec coordinates, on a Euclidean tangent plane, or in 3D using either (RA,Dec,r) or (x,y,z) positions.
The front end is in Python, which can be used as a Python module or as a standalone executable using configuration files. (The executable is corr2 for 2-point and corr3 for 3-point.)
The actual computation of the correlation functions is done in C++ using ball trees (similar to kd trees), which make the calculation extremely efficient.
When available, OpenMP is used to run in parallel on multi-core machines.
Approximate running time for 2-point shear-shear is ~30 sec * (N/10^6) / core for a bin size b=0.1 in log(r). It scales as b^(-2). This is the slowest of the various kinds of 2-point correlations, so others will be a bit faster, but with the same scaling with N and b.
The running time for 3-point functions are highly variable depending on the range of triangle geometries you are calculating. They are significantly slower than the 2-point functions, but many orders of magnitude faster than brute force algorithms.
Reference: Jarvis, Bernstein, & Jain, 2004, MNRAS, 352, 338 (I’m working on new paper about TreeCorr, including some of the improvements I’ve made since then, but this will suffice as a reference for now.)
Record on the Astrophyics Source Code Library: http://ascl.net/1508.007
The code is licensed under a FreeBSD license. Essentially, you can use the code in any way you want, but if you distribute it, you need to include the file TreeCorr_LICENSE with the distribution. See that file for details.
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