Cosmological Parameter Estimation from the CMB

Abstract

this paper. The modes are optimised for fi, and only the best 320 modes are used. We see that the conditional error in the fi direction is not much worse than the full set, but the likelihood declines slowly along the ridge, and the marginal errors on both fi and \Delta have increased substantially. In the panel bottom left, the SVD procedure has been applied to the union of modes optimised for fi and \Delta, keeping the best 320 modes. The procedure does reasonably well, but in this case the error along the ridge has increased. The bottom right graph shows the result of diagonalizing the Fisher matrix and optimising for the eigenvalue along the ridge. We see excellent behaviour for the best 320 modes, with almost no loss of information compared with the full set. This illustrative example shows how data compression may be achieved with good results by application of a combination of rigorous optimisation and a helping of common sense. 5 Conclusion