Spherical inhomogeneous cosmologies and inflation: Numerical methods

We describe a spherically symmetric code for inhomogeneous cosmological problems. Our main goal is to study the onset of inflation under inhomogeneous conditions. We would like to explore the influence of inhomogeneity on inflation. In particular we address the question of whether large inhomogeneity during the very early Universe can prevent the Universe from entering an inflationary era. In this paper we describe the equations, the numerical techniques, tests, and some preliminary results. A detailed discussion of the results will follow in a subsequent paper.