For the computation of the matrix ds-dcb, we compare the recursion dlss method (eq 15 of 'pixel covariance matrix' - M.Tristram) versus the explicite relation (eq 28)

  • Full sky, polar, 1 core.
  • MC Precision is computed as {$ \displaystyle \frac{diag(S_{analytic})}{std(diag(S_{mc}))} $}
Nsidedl_ss (15)explicite (28)Monte carlo
2~1 sec~0.9 sec~ 0.6 sec (10% precision on diag(S) )
4~29 sec~24 sec~ 9 sec (5 % precision)
8~1000 sec~700 sec~ 60 sec (2.5% precision)
16~32000 sec~24000 sec~ 1500 sec (? % precision not calculated)
  • Conclusion : explicit relation is faster (at least in python) than recursion method dlss.
  • Monte-carlo is highly competitive ! Number of simulations = 4*npix. Tests should be extended to compare the estimator variance between the MC and the analytical method.