36th 'example' file for CPO2D.

 A three-tube einzel lens.

 The z=0 plane  is a plane of voltage symmetry. 


 The outer cylinders extend from z=-6 to z=-0.55 and +6 to +0.55, while the inner cylinder extends from z=-0.45 to z=+0.45,  The radius of the cylinders is 0.5 and the outer ones are capped at their  far ends.  The charge density on the cylinders  is highest at the ends near the gap, so the segments into which the cylinders  are subdivided are made the smallest there (by using 'type 1' of subdivision,  as explained in note 12).


 The region from z=-4.8 to +4.8 is specified for obtaining the lens parameters, and this length is divided into 1000 steps. The requested value of the voltage ratio V2/V1 (which is essentially E2/E1) is 10.

 See notes on xmpl2d01 for a full description of how to obtain the highest  accuracy for the lens parameters.