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[CreaPhase.git] / octave_packages / control-2.3.52 / @frd / frd.m

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+## Copyright (C) 2010, 2011   Lukas F. Reichlin
+##
+## This file is part of LTI Syncope.
+##
+## LTI Syncope is free software: you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## LTI Syncope is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with LTI Syncope.  If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{sys} =} frd (@var{sys})
+## @deftypefnx {Function File} {@var{sys} =} frd (@var{sys}, @var{w})
+## @deftypefnx {Function File} {@var{sys} =} frd (@var{H}, @var{w}, @dots{})
+## @deftypefnx {Function File} {@var{sys} =} frd (@var{H}, @var{w}, @var{tsam}, @dots{})
+## Create or convert to frequency response data.
+##
+## @strong{Inputs}
+## @table @var
+## @item sys
+## LTI model to be converted to frequency response data.
+## If second argument @var{w} is omitted, the interesting
+## frequency range is calculated by the zeros and poles of @var{sys}.
+## @item H
+## Frequency response array (p-by-m-by-lw).  H(i,j,k) contains the
+## response from input j to output i at frequency k.  In the SISO case,
+## a vector (lw-by-1) or (1-by-lw) is accepted as well.
+## @item w
+## Frequency vector (lw-by-1) in radian per second [rad/s].
+## Frequencies must be in ascending order.
+## @item tsam
+## Sampling time in seconds.  If @var{tsam} is not specified,
+## a continuous-time model is assumed.
+## @item @dots{}
+## Optional pairs of properties and values.
+## Type @command{set (frd)} for more information.
+## @end table
+##
+## @strong{Outputs}
+## @table @var
+## @item sys
+## Frequency response data object.
+## @end table
+##
+## @seealso{dss, ss, tf}
+## @end deftypefn
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: February 2010
+## Version: 0.1
+
+function sys = frd (H = [], w = [], varargin)
+
+  ## NOTE: * There's no such thing as a static gain
+  ##         because FRD objects are measurements,
+  ##         not models.
+  ##       * If something like  sys1 = frd (5)  existed,
+  ##         it would cause troubles in cases like
+  ##         sys2 = ss (...), sys = sys1 * sys2
+  ##         because sys2 needs to be converted to FRD,
+  ##         but sys1 contains no valid frequencies.
+  ##       * However, things like  frd (ss (5))  should
+  ##         be possible.
+
+  ## model precedence: frd > ss > zpk > tf > double
+  superiorto ("ss", "zpk", "tf", "double");
+  
+  argc = 0;                             # initialize argument count
+
+  switch (nargin)
+    case 0                              # empty object  sys = frd ()
+      tsam = -2;                        # undefined sampling time
+
+    case 1
+      if (isa (H, "frd"))               # already in frd form  sys = frd (frdsys)
+        sys = H;
+        return;                         # nothing more to do here
+      elseif (isa (H, "lti"))           # another lti object  sys = frd (sys)
+        [sys, alti] = __sys2frd__ (H);
+        sys.lti = alti;                 # preserve lti properties
+        return;                         # nothing more to do here
+      else                              # sys = frd (H)  *must* fail
+        print_usage ();
+      endif
+
+    case 2
+      if (isa (H, "lti"))               # another lti object  sys = frd (sys, w)
+        [sys, alti] = __sys2frd__ (H, w);
+        sys.lti = alti;                 # preserve lti properties
+        return;                         # nothing more to do here
+      else                              # sys = frd (H, w)
+        tsam = 0;                       # continuous-time
+      endif
+
+    otherwise                           # default case
+      argc = numel (varargin);          # number of additional arguments after H and w
+      if (issample (varargin{1}, -10))  # sys = frd (H, w, tsam, "prop1", val1, ...)
+        tsam = varargin{1};             # sampling time, could be 0 as well
+        argc--;                         # tsam is not a property-value pair
+        if (argc > 0)                   # if there are any properties and values ...
+          varargin = varargin(2:end);   # remove tsam from property-value list
+        endif
+      else                              # sys = frd (H, w, "prop1", val1, ...)
+        tsam = 0;                       # continuous-time
+      endif
+  endswitch
+
+  [H, w] = __adjust_frd_data__ (H, w);
+  [p, m] = __frd_dim__ (H, w);          # determine number of outputs and inputs
+
+  frdata = struct ("H", H, "w", w);     # struct for frd-specific data
+  ltisys = lti (p, m, tsam);            # parent class for general lti data
+
+  sys = class (frdata, "frd", ltisys);  # create frd object
+
+  if (argc > 0)                         # if there are any properties and values, ...
+    sys = set (sys, varargin{:});       # use the general set function
+  endif
+
+endfunction