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   Perform actions specified by the HUD. Define a data structure

   global hUDOutput
   hUDOutput = struct('pushbutton1',0,'pushbutton2',0,'checkbox1',0,...
                      'checkbox2',0,'checkbox3',0)

   At the end of your simulation loop type

     HUDCntrl;
   end;

   This routine is called by a callback routine in HUD.m. You do not 
   normally call it yourself.

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   Form:
   HUDCntrl( action )
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   ------
   Inputs
   ------
   action    (1,:) Action to take

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

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