Using perturbative least action to recover cosmological initial conditions

We introduce a new method for generating initial conditions consistent with highly nonlinear observations of density and velocity fields. Using a vari ant of the least action method, called perturbative least action (PLA), we show that it is possible to generate several different sets of initial cond itions, each of which will satisfy a set of highly nonlinear observational constraints at the present day. We then discuss a code written to test and apply this method, and present the results of several simulations.