The model shape

This is the heart of the modification from the original 1-D stenholm program to the present 2-D ASTRA program. The 1-D version consists of a series of concentric shells. In this 2-D version the shells have been replaced by a system of disks and cylinders. The model can be viewed as a series of concentric cylinders which are cut at right angles by a series of planes, thus forming a set of stacked concentric rings each with a rectangular cross-section. The model is that part of the total space that is bounded by the lowest and uppermost plane and the outermost cylinder. This produces a cylindrical shaped model capped by two flat disks.

Throughout the program it is necessary to refer to the rings, cylinders and disks by numbers and therefore a consistent labelling system is important. The cylinders are labelled from 1 to $ncyls$ with label 0 being attached to the line of symmetry down the centre of the cloud. The disks are labelled from 0 to $ndisks-1$ with 0 being the lowest disk and $ndisks-1$ the uppermost. Thus there are $ncyls$ cylinders and $ndisks$ disks in the cloud. The rings are labeled from 1 to $ncyls \times (ndisks-1)$ starting with the lowest and innermost ring and then working outward and upward.