WindClass:

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   Wind class. 
   Returns information related to a U.S. wind class. Classes are from
   1 to 7. The information can be a 30 m or 50 m. Default is 30 m.

   Type

   WindClass

   for a demo

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   Form:
   [w, p] = WindClass( type, k, height )
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   ------
   Inputs
   ------
   type       (1,:) 'class' or 'speed'
   k          (1,1) Class number (1-7) or wind speed (m/s)
   height     (1,1) Height (m) can only be 30 or 50

   -------
   Outputs
   -------
   w          (1,1) If type == 'class' speed: [min, max] otherwise class
   p          (1,1) If type == 'class' power: [min, max]

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   Reference: http://www.windpower.org/en/stat/unitsw.htm#visco
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