SelectS:

--------------------------------------------------------------------------
   Extract selected states from a state space model.

   Since version 1.
--------------------------------------------------------------------------
   Form:
   [a, b, c, d] = SelectS( a, b, c, d, kS, kO, kI )
--------------------------------------------------------------------------

   ------
   Inputs
   ------
   a                   Plant matrix
   b                   Input matrix
   c                   Output matrix
   d                   Feedthrough matrix
   kS                  Selected states
   kO                  Selected outputs
   kI                  Selected inputs

   -------
   Outputs
   -------
   a                   Plant matrix
   b                   Input matrix
   c                   Output matrix
   d                   Feedthrough matrix

--------------------------------------------------------------------------