Normal:

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   Compute a normal from a set of vertices using the Newell method.

   Since version 2.
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   Form:
   n = Normal( v )
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   ------
   Inputs
   ------
   v             (3,:)   Polygon vertices

   -------
   Outputs
   -------
   n             (3,1)   Normal

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	References:	Hill, F. S. Jr., Computer Graphics, MacMillan, 1990,
               p. 258.
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