2-FAST: Fast and accurate computation of projected two-point functions
  We present the 2-point function from Fast and Accurate Spherical Bessel
Transformation (2-FAST) algorithm for a fast and accurate computation of
integrals involving one or two spherical Bessel functions. These types of
integrals occur when projecting the galaxy power spectrum $P(k)$ onto the
configuration space, $\xi_\ell^\nu(r)$, or spherical harmonic space,
$C_\ell(\chi,\chi')$. First, we employ the FFTlog transformation of the power
spectrum to divide the calculation into $P(k)$-dependent coefficients and
$P(k)$-independent integrations of basis functions multiplied by spherical
Bessel functions. We find analytical expressions for the latter integrals in
terms of special functions, for which recursion provides a fast and accurate
evaluation. The algorithm, therefore, circumvents direct integration of highly
oscillating spherical Bessel functions.
