Theory

FAST-PT Algorithm

FAST-PT is a numerical algorithm to calculate 1-loop contributions to the matter power spectrum and other integrals of a similar type. The method is presented in papers arXiv:1603.04826 and arXiv:1609.05978.

The core of the FAST-PT algorithm is to compute integrals of the form:

\[\int \frac{d^3q}{(2 \pi)^3} K(q,k-q) P(q) P(|k-q|)\]

by using Fourier transforms to reduce computational complexity from \(O(N^2)\) to \(O(N\\log N)\), where \(N\) is the number of input points.

For intrinsic alignment calculations, see arXiv:1708.09247.