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   Export fields required by DSim. This routine will create three files.

   fileName.obj  - geometry data (Wavefront format)
   fileName.mtl  - material data (Wavefront format)
   fileName.dss  - the DSim setup file

   If you enter a fileName the extension will be ignored.
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   Form:
   ExportDSim( g, fileName, default, package )
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   ------
   Inputs
   ------
   g           (:,:) CAD Data structure
   fileName    (1,:) Optional file name
   default     (1,:) Default object class
   package     (1,:) Package containing classes

   -------
   Outputs
   -------
   None

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