Fast and Exact Spin-s Spherical Harmonic Transforms
  We demonstrate a fast spin-s spherical harmonic transform algorithm, which is
flexible and exact for band-limited functions. In contrast to previous work,
where spin transforms are computed independently, our algorithm permits the
computation of several distinct spin transforms simultaneously. Specifically,
only one set of special functions is computed for transforms of quantities with
any spin, namely the Wigner d-matrices evaluated at {\pi}/2, which may be
computed with efficient recursions. For any spin the computation scales as
O(L^3) where L is the band-limit of the function. Our publicly available
numerical implementation permits very high accuracy at modest computational
cost. We discuss applications to the Cosmic Microwave Background (CMB) and
gravitational lensing.
