RECONSTRUCTION OF INITIAL COSMOLOGICAL DENSITY-FLUCTUATIONS BY THE PSEUDOSPECTRAL METHOD

The pseudospectral method is proposed for tracing the evolution of den sity and velocity fluctuations in the weakly nonlinear stage of the ex panding universe with good accuracy. In this method, the evolution of density and velocity fluctuations is integrated in Fourier space using the fast Fourier transformation. The method is well suited to an accu rate investigation of dynamics in weakly nonlinear evolution. Furtherm ore, one can recover primordial density and velocity fluctuations by i ntegrating the evolution of density and velocity fluctuations backward in time by the pseudospectral method, while using a fitting formula t o impose the relation between density and velocity fields that holds i n the weakly nonlinear regime.