SkewSq:

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   Computes the product of two skew symmetric matrices derive from vectors.
   If only one matrix is entered it will compute the square.

   Since version 2.
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   Form:
   s = SkewSq( v, u )
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   -----
   Input
   -----
   v               (3,1) Vector
   u               (3,1) Vector

   ------
   Output
   ------
   s               (3,3) Square of the skew matrix

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