SteadyS:

--------------------------------------------------------------------------
   Determine the steady state control for a state space system.
   .
   x = Ax + Bu
   y = Cx + Du

   given y. If the number of inputs is less than the number of 
   outputs it computes a weighted least squares fit to y using
   the weighting matrix q. If the number of inputs is greater
   than the number of outputs it minimizes the function u'ru. 
   If q is not input it uses the identity matrix.

   Since version 1.
--------------------------------------------------------------------------
   Form:
   [u, x, yC] = SteadyS( a, b, c, d, y, q, r )
--------------------------------------------------------------------------

   ------
   Inputs
   ------
   a                   Plant matrix
   b                   Input matrix
   c                   Output matrix
   d                   Feedthrough matrix
   y                   Desired output
   q                   Weighting matrix for y
   r                   Weighting matrix for u

   -------
   Outputs
   -------
   u                   Steady state control
   x                   Steady state state
   yC                  Achievable y if number of outputs > number of controls

--------------------------------------------------------------------------
	Reference:  Bryson, A.E., Jr. (1994). Control of Spacecraft and Aircraft
               Princeton University Press, Princeton, NJ.
--------------------------------------------------------------------------