A fast map-making preconditioner for regular scanning patterns
  High-resolution Maximum Likelihood map-making of the Cosmic Microwave
Background is usually performed using Conjugate Gradients with a preconditioner
that ignores noise correlations. We here present a new preconditioner that
approximates the map noise covariance as circulant, and show that this results
in a speedup of up to 400% for a realistic scanning pattern from the Atacama
Cosmology Telescope. The improvement is especially large for polarized maps.
