**encore: Efficient isotropic 2-, 3-, 4-, 5- and 6-point correlation functions**

**Abstract**: encore (Efficient <i>N</i>-point Correlator Estimation) estimates the isotropic NPCF multipoles for an arbitrary survey geometry in <i>O</i>(<i>N</i><sup>2</sup>) time, with optional GPU support. The code features support for the isotropic 2PCF, 3PCF, 4PCF, 5PCF and 6PCF, with the option to subtract the Gaussian 4PCF contributions at the estimator level. For the 4PCF, 5PCF and 6PCF algorithms, the runtime is dominated by sorting the spherical harmonics into bins, which has complexity <i>O</i>(<i>N</i>_galaxy x <i>N</i>_bins<sup>3</sup> x <i>N</i>_ell<sup>5</sup>) [4PCF], <i>O</i>(<i>N</i>_galaxy x N_bins<sup>4</sup> x N_ell<sup>8</sup>) [5PCF] or <i>O</i>(<i>N</i>_galaxy x <i>N</i>_bins<sup>5</sup> x <i>N</i>_ell<sup>11</sup>) [6PCF]. The higher-point functions are slow to compute unless <i>N</i>_bins and <i>N</i>_ell are small.

**Credit**: Philcox, Oliver H. E.; Slepian, Zachary; Hou, Jiamin; Warner, Craig; Cahn, Robert N.; Eisenstein, Daniel J.

**Site**: https://github.com/oliverphilcox/encore

https://ui.adsabs.harvard.edu/abs/2021arXiv210508722P

**Bibcode**: 2021ascl.soft05014P

**ID**: ascl:2105.014