Summary of important user-visible changes for releases of the control package

===============================================================================
control-2.2.0   Release Date: 2011-09-26   Release Manager: Lukas Reichlin
===============================================================================

** ss
   -- Transfer function to state-space conversion uses now SLICOT TD04AD.
      Conversion of MIMO models is now supported.  Usage: ss_sys = ss (tf_sys)

** tf
   -- Support for interconnections of MIMO transfer functions.  This is done by
      an internal conversion to a minimal state-space representation.  With the
      current tf2ss and ss2tf conversions, only proper transfer function are
      supported.  This limitation does not exist for SISO transfer functions.

** @lti/pole, @lti/zero
   -- Computation of poles and zeros of MIMO transfer functions is now possible
      via conversion to state-space.  Please note that the state-space
      realization of SLICOT TD04AD is a minimal one.  Therefore certain poles
      and zeros might be missing.

** zpk, @lti/zpkdata
   -- Included wrappers that create transfer function models from zero-pole-gain
      data (zpk) and zero-pole-gain data from lti models (zpkdata).  They are
      stop-gap measures for compatibility until ZPK models are implemented.

** @lti/tfdata
   -- "vector" option added.  For SISO models, it returns numerator and
      denominator directly as column vectors instead of cells containing a
      single column vector.

** doc/control.pdf
   -- Revised PDF manual.


===============================================================================
control-2.1.55   Release Date: 2011-09-07   Release Manager: Lukas Reichlin
===============================================================================

** @lti/c2d
   -- Support for "tustin" and "prewarp" method added.
   -- Transfer functions are now supported via the state-space methods.
   -- Improved Texinfo string.

** @lti/d2c
   -- Discrete to continuous-time conversion added.  However, support is
      limited to the zero-order hold, tustin and pre-warping methods.
   
** Conversion from descriptor to regular state-space is now performed by SLICOT
   routine SB10JD.  Better numerical results are to be expected over the
   previous naive inversion formula.  This conversion is used internally for
   ssdata and some other functions.


===============================================================================
control-2.1.54   Release Date: 2011-08-22   Release Manager: Lukas Reichlin
===============================================================================

** tf
   -- State-space to transfer function conversion uses now SLICOT TB04BD.
      Conversion of MIMO models is now supported.  Usage: tf_sys = tf (ss_sys)
   -- Display an empty line between title and numerator for better readability.
   -- Display whether model is static, continuous- or discrete-time.

** A PDF manual is included for the first time.  It is located inside the "doc"
   folder.  It has been generated automatically from the Texinfo help strings
   and is not yet completely sorted out.


===============================================================================
control-2.1.53   Release Date: 2011-08-08   Release Manager: Lukas Reichlin
===============================================================================

** ncfsyn
   -- Added support for McFarlane/Glover loop shaping design procedure.
      "ncfsyn" stands for Normalized Coprime Factor Synthesis.

** MDSSystem
   -- Added example script which demonstrates the usage of the robust control
      commands "mixsyn" and "ncfsyn".

** Texinfo help strings of several functions have been extended, although
   documentation still leaves a lot to be desired.


===============================================================================
control-2.1.52   Release Date: 2011-07-27   Release Manager: Lukas Reichlin
===============================================================================

** hsvd
   -- Use scaling unless state-space model property "scaled" is set to true.

** @lti/norm
   -- Use scaling for computation of L-infinity norm unless state-space model
      property "scaled" is set to true.
      
** @lti/minreal
   -- Use scaling for state-space and descriptor state-space models unless
      property "scaled" is set to true.
   -- More accurate results are to be expected for descriptor state-space
      models by performing only those reduction phases where effective order
      reduction occurs. This is achieved by saving the system matrices before
      each phase and restoring them if no order reduction took place.
  
** @lti/zero
   -- Use scaling for state-space and descriptor state-space models unless
      property "scaled" is set to true.

** @lti/frdata
   -- The frequency response is now returned correctly as an array and not as a
      vector, unless the "vector" option is set and the system is single-input
      single-output.
   -- Added help text.


===============================================================================
control-2.1.51   Release Date: 2011-07-21   Release Manager: Lukas Reichlin
===============================================================================

** frd
   -- Support for Frequency Response Data (frd) measurement "models".


===============================================================================
control-2.1.50   Release Date: 2011-07-06   Release Manager: Lukas Reichlin
===============================================================================

** ss
   -- Support for property "scaled".  By default, it is set to "false".

** @lti/prescale
   -- Scaling for state-space models (SLICOT TB01ID) and descriptor models
      (SLICOT TG01AD).
   
** @lti/freqresp
   -- Scale state-space models using @lti/prescale.m if property "scaled" is
      set to "false".  Frequency response commands now perform automatic
      scaling unless model property "scaled" is set to "true".


===============================================================================
control-2.0.2   Release Date: 2011-03-18   Release Manager: Lukas Reichlin
===============================================================================

** lsim
   -- Fixed a logical error that refused valid initial state vectors.  It was
      due to a thinko introduced with the changes in control-2.0.1.
      (Thanks to Rob Frohne)


===============================================================================
control-2.0.1   Release Date: 2011-03-06   Release Manager: Lukas Reichlin
===============================================================================

** lsim
   -- Support time vectors not starting at zero. (Thanks to Rob Frohne)
   -- Improved help text.

** @lti/zero
   -- The gain of descriptor state-space models is now computed correctly.
      (fingers crossed)


===============================================================================
control-2.0.0   Release Date: 2011-02-08   Release Manager: Lukas Reichlin
===============================================================================

** First official release.


===============================================================================
