SizeABCD:

--------------------------------------------------------------------------
   Checks the dimensions of the set a,b,c,d for consistency.
   d need not be input.

   Since version 1.
--------------------------------------------------------------------------
   Form:
   notok = SizeABCD( a, b, c, d )
--------------------------------------------------------------------------

   ------
   Inputs
   ------
   a                   Plant matrix
   b                   Input matrix
   c                   Measurement matrix
   d                   Input feedthrough matrix (optional)

   -------
   Outputs
   -------
   notok               Not correct if equal to 0

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